<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2024 Workiva-->
<!--r:8194df7f-b43b-40d4-9d4e-ead2f875034d,g:8ebda08c-b5f5-407a-96a5-1277d598dcd8-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.viantinc.com/role/CoverPage" xlink:type="simple" xlink:href="dsp-20240930.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_928031f6-a2aa-46a7-b971-86ffec17f656" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_DocumentInformationTable_928031f6-a2aa-46a7-b971-86ffec17f656" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_233830d5-03b2-4ad3-bf9c-e907ee76d331" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_928031f6-a2aa-46a7-b971-86ffec17f656" xlink:to="loc_us-gaap_StatementClassOfStockAxis_233830d5-03b2-4ad3-bf9c-e907ee76d331" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_233830d5-03b2-4ad3-bf9c-e907ee76d331_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_233830d5-03b2-4ad3-bf9c-e907ee76d331" xlink:to="loc_us-gaap_ClassOfStockDomain_233830d5-03b2-4ad3-bf9c-e907ee76d331_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_000237c4-a835-46d5-88c1-24650ea42a23" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_233830d5-03b2-4ad3-bf9c-e907ee76d331" xlink:to="loc_us-gaap_ClassOfStockDomain_000237c4-a835-46d5-88c1-24650ea42a23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_0d7e2dd8-5dec-4c0f-a3ef-501c2de9a255" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_000237c4-a835-46d5-88c1-24650ea42a23" xlink:to="loc_us-gaap_CommonClassAMember_0d7e2dd8-5dec-4c0f-a3ef-501c2de9a255" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_f9fe4185-531f-499f-8829-8c71dae963c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_000237c4-a835-46d5-88c1-24650ea42a23" xlink:to="loc_us-gaap_CommonClassBMember_f9fe4185-531f-499f-8829-8c71dae963c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_015d3a86-7f3c-4fa5-8c79-bab14075cd36" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_DocumentType_015d3a86-7f3c-4fa5-8c79-bab14075cd36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_1dbe17d2-4c9b-4d7d-981c-d71f1e32ab31" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_DocumentQuarterlyReport_1dbe17d2-4c9b-4d7d-981c-d71f1e32ab31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_f81bd4b6-1d86-488a-b457-88bde2911c6c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_DocumentPeriodEndDate_f81bd4b6-1d86-488a-b457-88bde2911c6c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_bd417dc2-1b4c-4d61-b3ed-947839429558" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_DocumentFiscalYearFocus_bd417dc2-1b4c-4d61-b3ed-947839429558" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_1c02d01a-7ced-4201-92bd-33cdb9f4578d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_DocumentTransitionReport_1c02d01a-7ced-4201-92bd-33cdb9f4578d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_5af4109c-78ba-4a3e-804c-8546e3ea6ac5" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityFileNumber_5af4109c-78ba-4a3e-804c-8546e3ea6ac5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_14a775e8-9d08-46b5-98fa-b05f32bcccac" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityRegistrantName_14a775e8-9d08-46b5-98fa-b05f32bcccac" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_ac4e11c7-e9a0-4745-8dbf-8185d5c5a637" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityIncorporationStateCountryCode_ac4e11c7-e9a0-4745-8dbf-8185d5c5a637" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_1f8066cc-cd2c-4bf7-a78f-3efb86dfdea9" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityTaxIdentificationNumber_1f8066cc-cd2c-4bf7-a78f-3efb86dfdea9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_32c2aca6-98aa-45ce-b801-9b1d281fd4c0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityAddressAddressLine1_32c2aca6-98aa-45ce-b801-9b1d281fd4c0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_7ef5151a-b56c-47fb-a613-916e9bafda9f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityAddressAddressLine2_7ef5151a-b56c-47fb-a613-916e9bafda9f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_95500a9f-3e31-4ce0-8e3c-62d63cfb13a9" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityAddressCityOrTown_95500a9f-3e31-4ce0-8e3c-62d63cfb13a9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_68ea7368-475e-4087-8d44-fe1f80d0a82d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityAddressStateOrProvince_68ea7368-475e-4087-8d44-fe1f80d0a82d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_1992bd4f-814e-47bf-be21-7e50b60f517f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityAddressPostalZipCode_1992bd4f-814e-47bf-be21-7e50b60f517f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_ae3c9809-2b19-426b-9299-a28e5ad49e20" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_CityAreaCode_ae3c9809-2b19-426b-9299-a28e5ad49e20" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_05681a45-f449-417f-8b2c-38e123439f64" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_LocalPhoneNumber_05681a45-f449-417f-8b2c-38e123439f64" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_e45ffff3-3db0-49a6-82e9-a500e324871f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_Security12bTitle_e45ffff3-3db0-49a6-82e9-a500e324871f" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_f30da9ee-cbac-42d3-a266-452ed22fe1e3" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_TradingSymbol_f30da9ee-cbac-42d3-a266-452ed22fe1e3" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_bf694f30-c9bb-4fa2-848f-7f7676012ad0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_SecurityExchangeName_bf694f30-c9bb-4fa2-848f-7f7676012ad0" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_8443cbd7-ca62-41ee-9bf9-a640384af314" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityCurrentReportingStatus_8443cbd7-ca62-41ee-9bf9-a640384af314" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_197ad067-324c-4702-8698-799f737d306e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityInteractiveDataCurrent_197ad067-324c-4702-8698-799f737d306e" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_e7866ea9-b93f-44a2-9613-46a55c1b4efe" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityFilerCategory_e7866ea9-b93f-44a2-9613-46a55c1b4efe" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_4bd1230e-0fc8-4d6b-8d8b-da98a23c5b07" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityEmergingGrowthCompany_4bd1230e-0fc8-4d6b-8d8b-da98a23c5b07" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_9f0a4e29-84c3-4407-a682-fdfcc31f444e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntitySmallBusiness_9f0a4e29-84c3-4407-a682-fdfcc31f444e" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_11157df0-237c-4ed2-a727-21127763b17f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityExTransitionPeriod_11157df0-237c-4ed2-a727-21127763b17f" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_65a5d4fd-684f-46bd-9868-a958c1a38790" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityShellCompany_65a5d4fd-684f-46bd-9868-a958c1a38790" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_9e209690-74a0-4d17-ab6b-079ab224a38a" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_9e209690-74a0-4d17-ab6b-079ab224a38a" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_45e0c706-046d-48e6-b616-06d472440ce4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_EntityCentralIndexKey_45e0c706-046d-48e6-b616-06d472440ce4" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_5029a54a-99f6-418e-8d4e-b1f37afeeae1" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_CurrentFiscalYearEndDate_5029a54a-99f6-418e-8d4e-b1f37afeeae1" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_d7b84a2b-bdec-4bab-a843-b336848dcd88" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_DocumentFiscalPeriodFocus_d7b84a2b-bdec-4bab-a843-b336848dcd88" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_0dfd9378-d458-4128-a1e6-8540b3362ac1" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_d5a7e6dd-754c-4e04-8b71-dc591c4f2321" xlink:to="loc_dei_AmendmentFlag_0dfd9378-d458-4128-a1e6-8540b3362ac1" xlink:type="arc" order="30"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="dsp-20240930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_7bdb3dd0-5541-44dd-b499-f9bb3bbaf267" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_d4b4b368-4e1d-4ff2-9773-cffff90a33c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7bdb3dd0-5541-44dd-b499-f9bb3bbaf267" xlink:to="loc_us-gaap_StatementTable_d4b4b368-4e1d-4ff2-9773-cffff90a33c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_2deea63b-c2e7-422c-8c0a-49b04e78f43b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d4b4b368-4e1d-4ff2-9773-cffff90a33c3" xlink:to="loc_us-gaap_StatementClassOfStockAxis_2deea63b-c2e7-422c-8c0a-49b04e78f43b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_2deea63b-c2e7-422c-8c0a-49b04e78f43b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_2deea63b-c2e7-422c-8c0a-49b04e78f43b" xlink:to="loc_us-gaap_ClassOfStockDomain_2deea63b-c2e7-422c-8c0a-49b04e78f43b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_884566ce-379c-4922-8ef5-5e5a37df92e7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_2deea63b-c2e7-422c-8c0a-49b04e78f43b" xlink:to="loc_us-gaap_ClassOfStockDomain_884566ce-379c-4922-8ef5-5e5a37df92e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_25059352-99fa-4244-9d6d-bbe743b391c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_884566ce-379c-4922-8ef5-5e5a37df92e7" xlink:to="loc_us-gaap_CommonClassAMember_25059352-99fa-4244-9d6d-bbe743b391c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_365b81f9-23ab-4734-94cc-9a7fac07d935" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_884566ce-379c-4922-8ef5-5e5a37df92e7" xlink:to="loc_us-gaap_CommonClassBMember_365b81f9-23ab-4734-94cc-9a7fac07d935" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7bdb3dd0-5541-44dd-b499-f9bb3bbaf267" xlink:to="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_0d115ccd-44f7-4a12-9555-5c5e56874c48" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:to="loc_us-gaap_AssetsCurrentAbstract_0d115ccd-44f7-4a12-9555-5c5e56874c48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_5b9cc0eb-744d-49a0-bf9b-67bddadbb362" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0d115ccd-44f7-4a12-9555-5c5e56874c48" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_5b9cc0eb-744d-49a0-bf9b-67bddadbb362" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_d9bb409d-931a-4f3f-9349-5dc44177b8be" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0d115ccd-44f7-4a12-9555-5c5e56874c48" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_d9bb409d-931a-4f3f-9349-5dc44177b8be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_d3e5d557-7146-4891-81ef-1726b4a69fab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0d115ccd-44f7-4a12-9555-5c5e56874c48" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_d3e5d557-7146-4891-81ef-1726b4a69fab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_ba12e6f0-5b4d-400f-a9b8-0260dfc6ec08" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0d115ccd-44f7-4a12-9555-5c5e56874c48" xlink:to="loc_us-gaap_AssetsCurrent_ba12e6f0-5b4d-400f-a9b8-0260dfc6ec08" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_563c7f6c-9c4a-4e85-96e0-4efe16162c5d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_563c7f6c-9c4a-4e85-96e0-4efe16162c5d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_f1391b38-a56c-445a-b012-e6df0ed3bc6d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_f1391b38-a56c-445a-b012-e6df0ed3bc6d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c54cd44f-464c-43af-9253-c393d00148e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c54cd44f-464c-43af-9253-c393d00148e0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_8ae8ca5e-d105-4660-bc87-b486e565f258" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:to="loc_us-gaap_Goodwill_8ae8ca5e-d105-4660-bc87-b486e565f258" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_ef10e12b-5556-4550-8f30-247b89ba105f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_ef10e12b-5556-4550-8f30-247b89ba105f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_0f33db36-3535-4f2f-b1d6-aea385c4d6e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2aecabb1-2a98-470e-97c1-da76c66e66a4" xlink:to="loc_us-gaap_Assets_0f33db36-3535-4f2f-b1d6-aea385c4d6e3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_1086f45a-eb36-42ed-86ea-5840c0cd9262" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7bdb3dd0-5541-44dd-b499-f9bb3bbaf267" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_1086f45a-eb36-42ed-86ea-5840c0cd9262" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_ed4208da-4e41-46a0-be6d-0f6490cd0137" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_1086f45a-eb36-42ed-86ea-5840c0cd9262" xlink:to="loc_us-gaap_LiabilitiesAbstract_ed4208da-4e41-46a0-be6d-0f6490cd0137" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_ed4208da-4e41-46a0-be6d-0f6490cd0137" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_568e90a3-c526-46e1-bb77-51b934b62778" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:to="loc_us-gaap_AccountsPayableCurrent_568e90a3-c526-46e1-bb77-51b934b62778" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_e0912c52-a38d-4ead-9bdb-edc8b7c02211" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_e0912c52-a38d-4ead-9bdb-edc8b7c02211" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedSalariesCurrent_5153d821-f28d-4b82-ab3a-9efcab932d3d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedSalariesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:to="loc_us-gaap_AccruedSalariesCurrent_5153d821-f28d-4b82-ab3a-9efcab932d3d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_7b9f8a83-1e05-41e1-9ac8-947acfa3404f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_7b9f8a83-1e05-41e1-9ac8-947acfa3404f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_65564f68-cf32-4cb2-ad84-318ca7c634d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_65564f68-cf32-4cb2-ad84-318ca7c634d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_7e8211aa-46e3-4c09-b27c-af73128446c0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_7e8211aa-46e3-4c09-b27c-af73128446c0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_cf1cc683-abd2-4c93-92ec-a635c9bb629f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_7da52ca2-6cce-49f1-bec0-71bc2f8ea305" xlink:to="loc_us-gaap_LiabilitiesCurrent_cf1cc683-abd2-4c93-92ec-a635c9bb629f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_ca55ffa8-6d4a-410b-850b-26a56e6aa00d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_ed4208da-4e41-46a0-be6d-0f6490cd0137" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_ca55ffa8-6d4a-410b-850b-26a56e6aa00d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_afcad1e6-e043-4147-8f24-3ad5114ff5eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_ed4208da-4e41-46a0-be6d-0f6490cd0137" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_afcad1e6-e043-4147-8f24-3ad5114ff5eb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_f0a5d7d4-6bc1-493c-bbb2-7884791f20eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_ed4208da-4e41-46a0-be6d-0f6490cd0137" xlink:to="loc_us-gaap_Liabilities_f0a5d7d4-6bc1-493c-bbb2-7884791f20eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_f028bb79-dc59-4b81-95a3-1ea0245267ba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_1086f45a-eb36-42ed-86ea-5840c0cd9262" xlink:to="loc_us-gaap_CommitmentsAndContingencies_f028bb79-dc59-4b81-95a3-1ea0245267ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_1086f45a-eb36-42ed-86ea-5840c0cd9262" xlink:to="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_84d62160-8ac2-4849-b41e-4df6230dae8c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_PreferredStockValue_84d62160-8ac2-4849-b41e-4df6230dae8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_bb185c7a-2e18-4fc4-a4ee-e84d49fb9799" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_CommonStockValue_bb185c7a-2e18-4fc4-a4ee-e84d49fb9799" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_2944f727-ec27-44ac-ac99-a5b9d916b02b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_AdditionalPaidInCapital_2944f727-ec27-44ac-ac99-a5b9d916b02b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_a1e0b1ae-84e4-4a4c-a4e4-88b5583ffa0b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_a1e0b1ae-84e4-4a4c-a4e4-88b5583ffa0b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValue_7c94fc14-3d23-4039-a7b2-02cd807c1f35" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TreasuryStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_TreasuryStockValue_7c94fc14-3d23-4039-a7b2-02cd807c1f35" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01e0c243-5da7-4845-a8b8-ce2e2cd5a2a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_StockholdersEquity_01e0c243-5da7-4845-a8b8-ce2e2cd5a2a2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_fd21a2e2-8b86-488b-ad92-70d68756e201" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_MinorityInterest_fd21a2e2-8b86-488b-ad92-70d68756e201" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_b17a44b9-17bb-41f1-b9f8-d5ff9992c267" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_924369c5-2930-448f-a584-ab243de0f55b" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_b17a44b9-17bb-41f1-b9f8-d5ff9992c267" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_e9798f6d-b9de-4aaf-8ba1-cf64f3275135" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_1086f45a-eb36-42ed-86ea-5840c0cd9262" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_e9798f6d-b9de-4aaf-8ba1-cf64f3275135" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="dsp-20240930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_ed4f8fce-86f8-48de-a24b-d30d7bfc586a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_StatementTable_ed4f8fce-86f8-48de-a24b-d30d7bfc586a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_8c43fa09-ebff-46d6-8910-7fa2937b0ccf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_ed4f8fce-86f8-48de-a24b-d30d7bfc586a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_8c43fa09-ebff-46d6-8910-7fa2937b0ccf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_8c43fa09-ebff-46d6-8910-7fa2937b0ccf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8c43fa09-ebff-46d6-8910-7fa2937b0ccf" xlink:to="loc_us-gaap_ClassOfStockDomain_8c43fa09-ebff-46d6-8910-7fa2937b0ccf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_34b1e2eb-4e82-4a55-913d-543820939b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8c43fa09-ebff-46d6-8910-7fa2937b0ccf" xlink:to="loc_us-gaap_ClassOfStockDomain_34b1e2eb-4e82-4a55-913d-543820939b7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_f753da45-13c5-433e-81ee-6ad66b38da99" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_34b1e2eb-4e82-4a55-913d-543820939b7c" xlink:to="loc_us-gaap_CommonClassAMember_f753da45-13c5-433e-81ee-6ad66b38da99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_77bedc2c-7551-4925-a011-d027b5263d19" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_34b1e2eb-4e82-4a55-913d-543820939b7c" xlink:to="loc_us-gaap_CommonClassBMember_77bedc2c-7551-4925-a011-d027b5263d19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_da003e46-3d10-4cfc-af57-b52d8b684bad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_da003e46-3d10-4cfc-af57-b52d8b684bad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_2e6ff0a5-5d4e-47c3-b22f-98e889fbcd26" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_2e6ff0a5-5d4e-47c3-b22f-98e889fbcd26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_a5d95d3c-027a-47fa-ab78-2d551e452607" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_PreferredStockSharesIssued_a5d95d3c-027a-47fa-ab78-2d551e452607" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_82395820-df7f-40e0-9f3b-92ca4289dd37" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_82395820-df7f-40e0-9f3b-92ca4289dd37" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_82670459-a24f-4e25-b520-ceee384f50ba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_82670459-a24f-4e25-b520-ceee384f50ba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_61ffda6d-0f0b-4fda-ba74-d1c3eede7d47" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_CommonStockValue_61ffda6d-0f0b-4fda-ba74-d1c3eede7d47" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_676443ef-c3d5-4909-b6a1-695e2a91b31e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_CommonStockSharesIssued_676443ef-c3d5-4909-b6a1-695e2a91b31e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_4f6047a0-fbe8-4eae-9b97-2844cfa070dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_4f6047a0-fbe8-4eae-9b97-2844cfa070dc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_2328128d-9832-4c7b-878b-43f84b2ba124" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5d906de-fcba-46c8-8212-84b1c4213e24" xlink:to="loc_us-gaap_TreasuryStockCommonShares_2328128d-9832-4c7b-878b-43f84b2ba124" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY" xlink:type="simple" xlink:href="dsp-20240930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_007556fd-bd08-46ea-8ae3-281eb3c7b186" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_41d3c7b4-ec2c-456f-818c-47e544222e81" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_007556fd-bd08-46ea-8ae3-281eb3c7b186" xlink:to="loc_us-gaap_StatementTable_41d3c7b4-ec2c-456f-818c-47e544222e81" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_8a480196-d9bc-4527-96be-90d893e7b2ce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_41d3c7b4-ec2c-456f-818c-47e544222e81" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_8a480196-d9bc-4527-96be-90d893e7b2ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8a480196-d9bc-4527-96be-90d893e7b2ce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8a480196-d9bc-4527-96be-90d893e7b2ce" xlink:to="loc_us-gaap_EquityComponentDomain_8a480196-d9bc-4527-96be-90d893e7b2ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f1ba7867-eeec-41c8-8f50-9fc781c17ee1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8a480196-d9bc-4527-96be-90d893e7b2ce" xlink:to="loc_us-gaap_EquityComponentDomain_f1ba7867-eeec-41c8-8f50-9fc781c17ee1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_9d6e038f-2b1f-4a12-8fad-26e75a82f339" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f1ba7867-eeec-41c8-8f50-9fc781c17ee1" xlink:to="loc_us-gaap_CommonStockMember_9d6e038f-2b1f-4a12-8fad-26e75a82f339" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_cfc010c8-5255-4f9d-9a52-6dd83d7034aa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f1ba7867-eeec-41c8-8f50-9fc781c17ee1" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_cfc010c8-5255-4f9d-9a52-6dd83d7034aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_3a6e83dd-757a-4280-8c77-b0c1579edf39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f1ba7867-eeec-41c8-8f50-9fc781c17ee1" xlink:to="loc_us-gaap_RetainedEarningsMember_3a6e83dd-757a-4280-8c77-b0c1579edf39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_aa26c211-2be3-4150-acbd-658d76784790" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f1ba7867-eeec-41c8-8f50-9fc781c17ee1" xlink:to="loc_us-gaap_TreasuryStockCommonMember_aa26c211-2be3-4150-acbd-658d76784790" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_8554947b-efc0-4c17-8e26-cbba0a6e557c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f1ba7867-eeec-41c8-8f50-9fc781c17ee1" xlink:to="loc_us-gaap_NoncontrollingInterestMember_8554947b-efc0-4c17-8e26-cbba0a6e557c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_ba31bc77-7e4c-463c-b2ea-c0358f25f9e8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_41d3c7b4-ec2c-456f-818c-47e544222e81" xlink:to="loc_us-gaap_StatementClassOfStockAxis_ba31bc77-7e4c-463c-b2ea-c0358f25f9e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ba31bc77-7e4c-463c-b2ea-c0358f25f9e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ba31bc77-7e4c-463c-b2ea-c0358f25f9e8" xlink:to="loc_us-gaap_ClassOfStockDomain_ba31bc77-7e4c-463c-b2ea-c0358f25f9e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_7026d391-0504-40a8-a4e1-5872d401f3d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ba31bc77-7e4c-463c-b2ea-c0358f25f9e8" xlink:to="loc_us-gaap_ClassOfStockDomain_7026d391-0504-40a8-a4e1-5872d401f3d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_6dce4170-6c68-4c90-af06-4817bc407cd0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7026d391-0504-40a8-a4e1-5872d401f3d3" xlink:to="loc_us-gaap_CommonClassAMember_6dce4170-6c68-4c90-af06-4817bc407cd0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_c2c21d14-f627-414b-865c-8f638d1675f0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7026d391-0504-40a8-a4e1-5872d401f3d3" xlink:to="loc_us-gaap_CommonClassBMember_c2c21d14-f627-414b-865c-8f638d1675f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_5d39c21d-41dd-41a4-a79b-a99ed5369ba1" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_41d3c7b4-ec2c-456f-818c-47e544222e81" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_5d39c21d-41dd-41a4-a79b-a99ed5369ba1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_5d39c21d-41dd-41a4-a79b-a99ed5369ba1_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_5d39c21d-41dd-41a4-a79b-a99ed5369ba1" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_5d39c21d-41dd-41a4-a79b-a99ed5369ba1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_cad7028d-da41-4547-bcf6-74ec12151a33" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_5d39c21d-41dd-41a4-a79b-a99ed5369ba1" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_cad7028d-da41-4547-bcf6-74ec12151a33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_a28ee77d-7a54-464c-ab4e-87e6c5044a23" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_cad7028d-da41-4547-bcf6-74ec12151a33" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_a28ee77d-7a54-464c-ab4e-87e6c5044a23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_30d9478f-2d61-4269-9af5-187c3738b2a2" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_cad7028d-da41-4547-bcf6-74ec12151a33" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_30d9478f-2d61-4269-9af5-187c3738b2a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdate201613Member_a9687dc8-9260-4e9a-ab2a-afa8dcfe4942" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountingStandardsUpdate201613Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_cad7028d-da41-4547-bcf6-74ec12151a33" xlink:to="loc_us-gaap_AccountingStandardsUpdate201613Member_a9687dc8-9260-4e9a-ab2a-afa8dcfe4942" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_007556fd-bd08-46ea-8ae3-281eb3c7b186" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_37ccef35-d730-491e-938e-fcb8cc59b135" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_SharesOutstanding_37ccef35-d730-491e-938e-fcb8cc59b135" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_ba5d3490-d83e-4d36-8144-043ff842d334" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_ba5d3490-d83e-4d36-8144-043ff842d334" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_b02cabe0-b05e-47c1-94f6-7bc9627b471a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_TreasuryStockCommonShares_b02cabe0-b05e-47c1-94f6-7bc9627b471a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_902bf9fc-d45a-4ce7-9abd-2bf692691eb4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_902bf9fc-d45a-4ce7-9abd-2bf692691eb4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeBenefitPlan_6d8340e8-f26f-4240-ab5e-15b40effb474" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeBenefitPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeBenefitPlan_6d8340e8-f26f-4240-ab5e-15b40effb474" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan_c172eddd-d2c9-4345-a28e-995280beae0f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan_c172eddd-d2c9-4345-a28e-995280beae0f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_5f4947e8-0f5b-4a6d-bb69-a897a8572014" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_5f4947e8-0f5b-4a6d-bb69-a897a8572014" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_ef50500d-ee89-443e-ae74-72174285d1c7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_ef50500d-ee89-443e-ae74-72174285d1c7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_3f41157e-30ff-41f2-974d-3db4ec2738d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_3f41157e-30ff-41f2-974d-3db4ec2738d4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_13194eee-cd64-4296-be7d-5a8655c3e2ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_13194eee-cd64-4296-be7d-5a8655c3e2ed" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_d94cbb5c-6057-4473-90e2-576751a8041e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_d94cbb5c-6057-4473-90e2-576751a8041e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_46957e32-1195-4f4d-918b-2ea70eab5513" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_46957e32-1195-4f4d-918b-2ea70eab5513" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_49b4e7e4-cee8-4838-b6ab-4e164166c91f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_49b4e7e4-cee8-4838-b6ab-4e164166c91f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued_c25abdbc-60fb-423d-b798-b444ce6fb727" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued_c25abdbc-60fb-423d-b798-b444ce6fb727" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_StockIssuedDuringPeriodValueAllocationOfEquityToNonControllingInterests_fc735764-fb7b-4844-b6d7-0a536fc0f1b7" xlink:href="dsp-20240930.xsd#dsp_StockIssuedDuringPeriodValueAllocationOfEquityToNonControllingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_dsp_StockIssuedDuringPeriodValueAllocationOfEquityToNonControllingInterests_fc735764-fb7b-4844-b6d7-0a536fc0f1b7" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_AdjustmentsToAdditionalPaidInCapitalAccruedMemberTaxDistributions_0125bb93-27bb-4171-8df7-7dca9b50aff3" xlink:href="dsp-20240930.xsd#dsp_AdjustmentsToAdditionalPaidInCapitalAccruedMemberTaxDistributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_dsp_AdjustmentsToAdditionalPaidInCapitalAccruedMemberTaxDistributions_0125bb93-27bb-4171-8df7-7dca9b50aff3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_4e8600b4-94c5-47fa-8103-d60892f25af5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_4e8600b4-94c5-47fa-8103-d60892f25af5" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_68c50f84-03a1-4f1e-9d31-faa47d33a94e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_eece1de4-0dda-4bcc-8caa-bbea86dd1bcb" xlink:to="loc_us-gaap_ProfitLoss_68c50f84-03a1-4f1e-9d31-faa47d33a94e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_59c1ce6e-5d27-4fb6-bf63-da72d21a11f3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_6094b584-8ce8-4ef6-8f8a-8b0e52dfffda" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_0a240d5c-111b-4144-ac2a-9ef784067ff2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TreasuryStockCommonShares"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/NatureofOperationsAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#NatureofOperationsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/NatureofOperationsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:href="dsp-20240930.xsd#dsp_NatureOfOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_NatureOfOperationsTable_49f392d3-3447-4389-8c99-261372c51d26" xlink:href="dsp-20240930.xsd#dsp_NatureOfOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_NatureOfOperationsTable_49f392d3-3447-4389-8c99-261372c51d26" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_a6a3cca6-5472-487d-b5d6-ce23d16c35e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dsp_NatureOfOperationsTable_49f392d3-3447-4389-8c99-261372c51d26" xlink:to="loc_us-gaap_StatementClassOfStockAxis_a6a3cca6-5472-487d-b5d6-ce23d16c35e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a6a3cca6-5472-487d-b5d6-ce23d16c35e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a6a3cca6-5472-487d-b5d6-ce23d16c35e0" xlink:to="loc_us-gaap_ClassOfStockDomain_a6a3cca6-5472-487d-b5d6-ce23d16c35e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_bb7f4838-5eb9-4e05-92de-b75f511dd1fb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a6a3cca6-5472-487d-b5d6-ce23d16c35e0" xlink:to="loc_us-gaap_ClassOfStockDomain_bb7f4838-5eb9-4e05-92de-b75f511dd1fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_b5f5064b-3fbf-4c4d-b84f-14cbe45f4b9f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_bb7f4838-5eb9-4e05-92de-b75f511dd1fb" xlink:to="loc_us-gaap_CommonClassAMember_b5f5064b-3fbf-4c4d-b84f-14cbe45f4b9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_3f677722-8499-4975-9c06-f4b2398ea63c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_bb7f4838-5eb9-4e05-92de-b75f511dd1fb" xlink:to="loc_us-gaap_CommonClassBMember_3f677722-8499-4975-9c06-f4b2398ea63c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ContinuingMembersClassBUnitsMember_c830d871-a9b0-4392-aeac-ee0098d55780" xlink:href="dsp-20240930.xsd#dsp_ContinuingMembersClassBUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_bb7f4838-5eb9-4e05-92de-b75f511dd1fb" xlink:to="loc_dsp_ContinuingMembersClassBUnitsMember_c830d871-a9b0-4392-aeac-ee0098d55780" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_MembersEquityClassAUnitsMember_598cc44e-a092-4d01-891a-7627c757d4aa" xlink:href="dsp-20240930.xsd#dsp_MembersEquityClassAUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_bb7f4838-5eb9-4e05-92de-b75f511dd1fb" xlink:to="loc_dsp_MembersEquityClassAUnitsMember_598cc44e-a092-4d01-891a-7627c757d4aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_21ccfc76-1d3c-4cfe-946b-29a523f5814f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dsp_NatureOfOperationsTable_49f392d3-3447-4389-8c99-261372c51d26" xlink:to="loc_srt_OwnershipAxis_21ccfc76-1d3c-4cfe-946b-29a523f5814f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_21ccfc76-1d3c-4cfe-946b-29a523f5814f_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_21ccfc76-1d3c-4cfe-946b-29a523f5814f" xlink:to="loc_srt_OwnershipDomain_21ccfc76-1d3c-4cfe-946b-29a523f5814f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_490dfa9b-0a33-4131-a1e1-e486486a5c5c" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_21ccfc76-1d3c-4cfe-946b-29a523f5814f" xlink:to="loc_srt_OwnershipDomain_490dfa9b-0a33-4131-a1e1-e486486a5c5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ViantTechnologyLLCMember_3796ec8a-6a8f-44fa-92ea-ac75627cea4d" xlink:href="dsp-20240930.xsd#dsp_ViantTechnologyLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_490dfa9b-0a33-4131-a1e1-e486486a5c5c" xlink:to="loc_dsp_ViantTechnologyLLCMember_3796ec8a-6a8f-44fa-92ea-ac75627cea4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_6c0aabff-06f7-4681-bcab-414d1b78745b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dsp_NatureOfOperationsTable_49f392d3-3447-4389-8c99-261372c51d26" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_6c0aabff-06f7-4681-bcab-414d1b78745b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_6c0aabff-06f7-4681-bcab-414d1b78745b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_6c0aabff-06f7-4681-bcab-414d1b78745b" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_6c0aabff-06f7-4681-bcab-414d1b78745b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c8939d9e-6276-491f-a80f-4dc970e6378f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_6c0aabff-06f7-4681-bcab-414d1b78745b" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c8939d9e-6276-491f-a80f-4dc970e6378f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_fa68d512-08cd-4620-82a4-3327f652c057" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c8939d9e-6276-491f-a80f-4dc970e6378f" xlink:to="loc_us-gaap_OverAllotmentOptionMember_fa68d512-08cd-4620-82a4-3327f652c057" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_9c74ce1e-bbe9-439e-96d3-285b3b73de63" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_9c74ce1e-bbe9-439e-96d3-285b3b73de63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_75e38475-e709-4f70-b377-9f1e0e675006" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_75e38475-e709-4f70-b377-9f1e0e675006" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ContinuingMembersExchangeBasis_1a638439-2579-45f9-a3f3-463386df4fc6" xlink:href="dsp-20240930.xsd#dsp_ContinuingMembersExchangeBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_ContinuingMembersExchangeBasis_1a638439-2579-45f9-a3f3-463386df4fc6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonUnitOutstanding_c8b3412f-7176-44de-809f-414c198aa9fb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonUnitOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_CommonUnitOutstanding_c8b3412f-7176-44de-809f-414c198aa9fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_CommonStockSharesIssuedForEachMembershipUnit_af5d4370-7589-4dcc-a766-08c21f31d92d" xlink:href="dsp-20240930.xsd#dsp_CommonStockSharesIssuedForEachMembershipUnit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_CommonStockSharesIssuedForEachMembershipUnit_af5d4370-7589-4dcc-a766-08c21f31d92d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_55782ea8-8a97-45db-96de-1e27a6b82a60" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_55782ea8-8a97-45db-96de-1e27a6b82a60" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_7c002dbe-404e-4243-9815-1e839f73db7f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_7c002dbe-404e-4243-9815-1e839f73db7f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_a70a6e99-24aa-4297-a22f-5060e412715e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_a70a6e99-24aa-4297-a22f-5060e412715e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_67ee0bd9-3640-4608-b883-41667d7c9c57" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_67ee0bd9-3640-4608-b883-41667d7c9c57" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_1c7bf773-2e76-46b1-b6d9-f9d207b65c38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_1c7bf773-2e76-46b1-b6d9-f9d207b65c38" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_PaymentsToAcquireMemberUnits_a21d56f2-1602-49b6-a493-a284cba93d51" xlink:href="dsp-20240930.xsd#dsp_PaymentsToAcquireMemberUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_PaymentsToAcquireMemberUnits_a21d56f2-1602-49b6-a493-a284cba93d51" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_MembersEquityUnitsAcquiredDuringPeriod_b53ce574-9c12-4bb9-96f5-608bd760b5e9" xlink:href="dsp-20240930.xsd#dsp_MembersEquityUnitsAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_MembersEquityUnitsAcquiredDuringPeriod_b53ce574-9c12-4bb9-96f5-608bd760b5e9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_StockIssuedDuringPeriodSharesUnderwritesOptionsExercised_4e3add79-7982-4ad1-b4f9-848985bdead0" xlink:href="dsp-20240930.xsd#dsp_StockIssuedDuringPeriodSharesUnderwritesOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_StockIssuedDuringPeriodSharesUnderwritesOptionsExercised_4e3add79-7982-4ad1-b4f9-848985bdead0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_MembersEquityUnitsReceivedDuringPeriodConversionOfUnits_954c4516-f383-48b9-851f-40917a5b43af" xlink:href="dsp-20240930.xsd#dsp_MembersEquityUnitsReceivedDuringPeriodConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_MembersEquityUnitsReceivedDuringPeriodConversionOfUnits_954c4516-f383-48b9-851f-40917a5b43af" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_CommonStockVotingRightsPercentage_2f209ed3-2034-4bd4-a426-1daea278485e" xlink:href="dsp-20240930.xsd#dsp_CommonStockVotingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_CommonStockVotingRightsPercentage_2f209ed3-2034-4bd4-a426-1daea278485e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_PercentageOfVotingRightsOfOutstandingCommonStock_0e2ac177-780a-40a6-97ce-4e6a82030acf" xlink:href="dsp-20240930.xsd#dsp_PercentageOfVotingRightsOfOutstandingCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_NatureOfOperationsLineItems_f7dc8707-2874-4be4-aa6d-6ca47b4a00d7" xlink:to="loc_dsp_PercentageOfVotingRightsOfOutstandingCommonStock_0e2ac177-780a-40a6-97ce-4e6a82030acf" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesSummaryofChangesinAllowanceforDoubtfulAccountsDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesSummaryofChangesinAllowanceforDoubtfulAccountsDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesSummaryofChangesinAllowanceforDoubtfulAccountsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_64432d5e-adbf-4fc9-bcba-5b8f7a5275e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_5dead8c9-ae93-499c-86fc-2bbc406e9221" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_64432d5e-adbf-4fc9-bcba-5b8f7a5275e0" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_5dead8c9-ae93-499c-86fc-2bbc406e9221" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_780d6e8e-6363-4f0d-9939-bb3b7eaaa898" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_5dead8c9-ae93-499c-86fc-2bbc406e9221" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_780d6e8e-6363-4f0d-9939-bb3b7eaaa898" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_780d6e8e-6363-4f0d-9939-bb3b7eaaa898_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_780d6e8e-6363-4f0d-9939-bb3b7eaaa898" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_780d6e8e-6363-4f0d-9939-bb3b7eaaa898_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a2dcc780-c080-4eaf-9759-aae8c1681c3b" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_780d6e8e-6363-4f0d-9939-bb3b7eaaa898" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a2dcc780-c080-4eaf-9759-aae8c1681c3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_b2110d23-70db-45e1-9e1e-892f527564a8" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a2dcc780-c080-4eaf-9759-aae8c1681c3b" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_b2110d23-70db-45e1-9e1e-892f527564a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_a108eb5a-ef24-452c-8e23-9e9599df8e90" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_64432d5e-adbf-4fc9-bcba-5b8f7a5275e0" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_a108eb5a-ef24-452c-8e23-9e9599df8e90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_88113265-2e06-4e58-a6fc-b0962ee0c8a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_a108eb5a-ef24-452c-8e23-9e9599df8e90" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_88113265-2e06-4e58-a6fc-b0962ee0c8a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_695a585c-698a-40de-9bba-203d4afc67a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_a108eb5a-ef24-452c-8e23-9e9599df8e90" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_695a585c-698a-40de-9bba-203d4afc67a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_d73bb4cc-7e63-4595-ab59-9ee6982a1fee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_a108eb5a-ef24-452c-8e23-9e9599df8e90" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_d73bb4cc-7e63-4595-ab59-9ee6982a1fee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_ae75d0ee-b4a0-4563-b298-53a5a85a0b0e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesLineItems_2cced8d1-0be2-4526-b083-867c598335f1" xlink:href="dsp-20240930.xsd#dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_7f2a2fcf-68a5-4e4d-9c13-6d217e6a5493" xlink:href="dsp-20240930.xsd#dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesLineItems_2cced8d1-0be2-4526-b083-867c598335f1" xlink:to="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_7f2a2fcf-68a5-4e4d-9c13-6d217e6a5493" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_3d0f6778-099c-4000-ac24-5e500a99f909" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_7f2a2fcf-68a5-4e4d-9c13-6d217e6a5493" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_3d0f6778-099c-4000-ac24-5e500a99f909" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_3d0f6778-099c-4000-ac24-5e500a99f909_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_3d0f6778-099c-4000-ac24-5e500a99f909" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_3d0f6778-099c-4000-ac24-5e500a99f909_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_0fcc2239-3aea-4f53-9bef-c389cfed440f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_3d0f6778-099c-4000-ac24-5e500a99f909" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_0fcc2239-3aea-4f53-9bef-c389cfed440f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_ae776b2c-ec10-487a-adcc-6de579f57ce3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_0fcc2239-3aea-4f53-9bef-c389cfed440f" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_ae776b2c-ec10-487a-adcc-6de579f57ce3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_31f1ae4b-e2de-40bb-a0cb-43c2f78e1b6c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplierConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_0fcc2239-3aea-4f53-9bef-c389cfed440f" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_31f1ae4b-e2de-40bb-a0cb-43c2f78e1b6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromRightsConcentrationRiskMember_519622ac-5373-4b8a-859e-2b278240657f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromRightsConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_0fcc2239-3aea-4f53-9bef-c389cfed440f" xlink:to="loc_us-gaap_RevenueFromRightsConcentrationRiskMember_519622ac-5373-4b8a-859e-2b278240657f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_099adda7-a1a3-426f-88e8-414e7dd39764" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_7f2a2fcf-68a5-4e4d-9c13-6d217e6a5493" xlink:to="loc_srt_MajorCustomersAxis_099adda7-a1a3-426f-88e8-414e7dd39764" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_099adda7-a1a3-426f-88e8-414e7dd39764_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_099adda7-a1a3-426f-88e8-414e7dd39764" xlink:to="loc_srt_NameOfMajorCustomerDomain_099adda7-a1a3-426f-88e8-414e7dd39764_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_099adda7-a1a3-426f-88e8-414e7dd39764" xlink:to="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_CustomerOneMember_f9da7c0a-e404-4f6b-95aa-22d906f43b3a" xlink:href="dsp-20240930.xsd#dsp_CustomerOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:to="loc_dsp_CustomerOneMember_f9da7c0a-e404-4f6b-95aa-22d906f43b3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_CustomerTwoMember_364eb07d-fc10-48ab-a57c-c5259b71aca0" xlink:href="dsp-20240930.xsd#dsp_CustomerTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:to="loc_dsp_CustomerTwoMember_364eb07d-fc10-48ab-a57c-c5259b71aca0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_AdvertisingAgencyHoldingCompanyOneMember_6d25d757-8a82-4144-b30c-51db6fa8dc3c" xlink:href="dsp-20240930.xsd#dsp_AdvertisingAgencyHoldingCompanyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:to="loc_dsp_AdvertisingAgencyHoldingCompanyOneMember_6d25d757-8a82-4144-b30c-51db6fa8dc3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_IndividualCustomerBMember_6a29503c-702e-4426-8684-42b26425d9a3" xlink:href="dsp-20240930.xsd#dsp_IndividualCustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:to="loc_dsp_IndividualCustomerBMember_6a29503c-702e-4426-8684-42b26425d9a3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_IndividualCustomerCMember_0cdb5e2e-77ef-4966-b757-8f22f47510ec" xlink:href="dsp-20240930.xsd#dsp_IndividualCustomerCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:to="loc_dsp_IndividualCustomerCMember_0cdb5e2e-77ef-4966-b757-8f22f47510ec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_IndividualCustomerDMember_5348a77c-d315-47b3-8613-441190ed83ff" xlink:href="dsp-20240930.xsd#dsp_IndividualCustomerDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d3347fa7-20f1-42f7-8c12-101337177aec" xlink:to="loc_dsp_IndividualCustomerDMember_5348a77c-d315-47b3-8613-441190ed83ff" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_df7980de-c115-47d8-be10-161783e26d77" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_7f2a2fcf-68a5-4e4d-9c13-6d217e6a5493" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_df7980de-c115-47d8-be10-161783e26d77" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_df7980de-c115-47d8-be10-161783e26d77_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_df7980de-c115-47d8-be10-161783e26d77" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_df7980de-c115-47d8-be10-161783e26d77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8b78deec-1bf3-47bc-88b6-deb1f24bad4d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_df7980de-c115-47d8-be10-161783e26d77" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8b78deec-1bf3-47bc-88b6-deb1f24bad4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_de3a7be3-2374-4ca2-b1e6-42f70ee999d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8b78deec-1bf3-47bc-88b6-deb1f24bad4d" xlink:to="loc_us-gaap_AccountsReceivableMember_de3a7be3-2374-4ca2-b1e6-42f70ee999d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_AccountsPayableAndAccruedLiabilitiesCurrentMember_d6349c0d-4b93-4c16-b44a-26b6f4171efb" xlink:href="dsp-20240930.xsd#dsp_AccountsPayableAndAccruedLiabilitiesCurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8b78deec-1bf3-47bc-88b6-deb1f24bad4d" xlink:to="loc_dsp_AccountsPayableAndAccruedLiabilitiesCurrentMember_d6349c0d-4b93-4c16-b44a-26b6f4171efb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_ec502b07-d8b0-4ff8-aa6c-c36a187f7291" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8b78deec-1bf3-47bc-88b6-deb1f24bad4d" xlink:to="loc_us-gaap_SalesRevenueNetMember_ec502b07-d8b0-4ff8-aa6c-c36a187f7291" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_7550c910-8974-4972-9441-291e798d188c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_7f2a2fcf-68a5-4e4d-9c13-6d217e6a5493" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_7550c910-8974-4972-9441-291e798d188c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_7550c910-8974-4972-9441-291e798d188c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_7550c910-8974-4972-9441-291e798d188c" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_7550c910-8974-4972-9441-291e798d188c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_8e576a28-0503-4633-ab87-6346be8240c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_7550c910-8974-4972-9441-291e798d188c" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_8e576a28-0503-4633-ab87-6346be8240c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_SupplierOneMember_d86d4052-31a9-470a-b3b1-0b2e4289dbed" xlink:href="dsp-20240930.xsd#dsp_SupplierOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_8e576a28-0503-4633-ab87-6346be8240c3" xlink:to="loc_dsp_SupplierOneMember_d86d4052-31a9-470a-b3b1-0b2e4289dbed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_SupplierTwoMember_6976fb44-d295-4e8a-ba84-c41fef5f5f76" xlink:href="dsp-20240930.xsd#dsp_SupplierTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_8e576a28-0503-4633-ab87-6346be8240c3" xlink:to="loc_dsp_SupplierTwoMember_6976fb44-d295-4e8a-ba84-c41fef5f5f76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_SupplierThreeMember_da92a4cc-47a5-4184-b44c-92f76f2332b0" xlink:href="dsp-20240930.xsd#dsp_SupplierThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_8e576a28-0503-4633-ab87-6346be8240c3" xlink:to="loc_dsp_SupplierThreeMember_da92a4cc-47a5-4184-b44c-92f76f2332b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsAtCarryingValue_6ac55235-b854-4fbb-a4c4-f6c799de9055" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MoneyMarketFundsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesLineItems_2cced8d1-0be2-4526-b083-867c598335f1" xlink:to="loc_us-gaap_MoneyMarketFundsAtCarryingValue_6ac55235-b854-4fbb-a4c4-f6c799de9055" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_faa67c5c-fedd-486d-bddd-f8e19bbc885f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesLineItems_2cced8d1-0be2-4526-b083-867c598335f1" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_faa67c5c-fedd-486d-bddd-f8e19bbc885f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/RevenueSummaryofDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#RevenueSummaryofDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/RevenueSummaryofDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_c1450bf3-6ec9-4d40-9444-7009b9285d1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_725be890-f6f1-4549-9cd8-5abf06576bba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_c1450bf3-6ec9-4d40-9444-7009b9285d1a" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_725be890-f6f1-4549-9cd8-5abf06576bba" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_d6e46582-f8b7-4cc9-9e3e-3b90ac361c8b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_725be890-f6f1-4549-9cd8-5abf06576bba" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_d6e46582-f8b7-4cc9-9e3e-3b90ac361c8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_d6e46582-f8b7-4cc9-9e3e-3b90ac361c8b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_d6e46582-f8b7-4cc9-9e3e-3b90ac361c8b" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_d6e46582-f8b7-4cc9-9e3e-3b90ac361c8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_29f03772-3c2b-469b-9d20-f75680447cbb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_d6e46582-f8b7-4cc9-9e3e-3b90ac361c8b" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_29f03772-3c2b-469b-9d20-f75680447cbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_ee991b8c-6bbf-4b2e-bd6e-39aa65725109" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_29f03772-3c2b-469b-9d20-f75680447cbb" xlink:to="loc_us-gaap_TransferredOverTimeMember_ee991b8c-6bbf-4b2e-bd6e-39aa65725109" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_e37fe4c1-83cd-49c4-a8f1-444ee33e5630" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_29f03772-3c2b-469b-9d20-f75680447cbb" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_e37fe4c1-83cd-49c4-a8f1-444ee33e5630" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f00f4cfb-02b0-4b39-a7f9-973ac2369850" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_c1450bf3-6ec9-4d40-9444-7009b9285d1a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f00f4cfb-02b0-4b39-a7f9-973ac2369850" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/RevenueAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#RevenueAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/RevenueAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_87a7e175-5256-4aac-b081-da773595e910" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_678fe0ed-bdc4-4c56-b721-f437f8184ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_87a7e175-5256-4aac-b081-da773595e910" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_678fe0ed-bdc4-4c56-b721-f437f8184ce6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerDurationAxis_3c260322-3c9b-4f59-8b7e-060149675424" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerDurationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_678fe0ed-bdc4-4c56-b721-f437f8184ce6" xlink:to="loc_us-gaap_ContractWithCustomerDurationAxis_3c260322-3c9b-4f59-8b7e-060149675424" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerDurationDomain_3c260322-3c9b-4f59-8b7e-060149675424_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerDurationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerDurationAxis_3c260322-3c9b-4f59-8b7e-060149675424" xlink:to="loc_us-gaap_ContractWithCustomerDurationDomain_3c260322-3c9b-4f59-8b7e-060149675424_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerDurationDomain_1f4265a1-c4d6-4aeb-bd44-1bde5220f38c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerDurationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerDurationAxis_3c260322-3c9b-4f59-8b7e-060149675424" xlink:to="loc_us-gaap_ContractWithCustomerDurationDomain_1f4265a1-c4d6-4aeb-bd44-1bde5220f38c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermContractWithCustomerMember_04d5029a-1138-4585-8b98-0f3d5567a49d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerDurationDomain_1f4265a1-c4d6-4aeb-bd44-1bde5220f38c" xlink:to="loc_us-gaap_LongTermContractWithCustomerMember_04d5029a-1138-4585-8b98-0f3d5567a49d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_996c34de-1098-4e3a-a6af-9348684f8705" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_87a7e175-5256-4aac-b081-da773595e910" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_996c34de-1098-4e3a-a6af-9348684f8705" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/PropertyEquipmentandSoftwareNetScheduleofMajorClassesofPropertyEquipmentandSoftwareDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#PropertyEquipmentandSoftwareNetScheduleofMajorClassesofPropertyEquipmentandSoftwareDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/PropertyEquipmentandSoftwareNetScheduleofMajorClassesofPropertyEquipmentandSoftwareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d6120c89-a145-4172-aed5-c1722e8bd1f8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_9b076f53-0d33-4471-b7e8-875bc98449a5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d6120c89-a145-4172-aed5-c1722e8bd1f8" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_9b076f53-0d33-4471-b7e8-875bc98449a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b819ad50-3d6e-4c62-b60c-ca30c8242079" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_9b076f53-0d33-4471-b7e8-875bc98449a5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b819ad50-3d6e-4c62-b60c-ca30c8242079" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b819ad50-3d6e-4c62-b60c-ca30c8242079_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b819ad50-3d6e-4c62-b60c-ca30c8242079" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b819ad50-3d6e-4c62-b60c-ca30c8242079_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6939e8de-af07-4e38-afad-f0fe0937698f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b819ad50-3d6e-4c62-b60c-ca30c8242079" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6939e8de-af07-4e38-afad-f0fe0937698f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_CapitalizedSoftwareDevelopmentCostsMember_3bb1194f-06df-4891-aaab-96ac43ea2253" xlink:href="dsp-20240930.xsd#dsp_CapitalizedSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6939e8de-af07-4e38-afad-f0fe0937698f" xlink:to="loc_dsp_CapitalizedSoftwareDevelopmentCostsMember_3bb1194f-06df-4891-aaab-96ac43ea2253" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_1300323d-7793-4572-9131-de585219a3eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6939e8de-af07-4e38-afad-f0fe0937698f" xlink:to="loc_us-gaap_ComputerEquipmentMember_1300323d-7793-4572-9131-de585219a3eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_e6493dac-bfed-4de0-ac84-262714a751b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6939e8de-af07-4e38-afad-f0fe0937698f" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_e6493dac-bfed-4de0-ac84-262714a751b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_FurnitureFixturesAndOfficeEquipmentMember_51a9b4e5-5d00-453f-9f3f-3ad606cad8c7" xlink:href="dsp-20240930.xsd#dsp_FurnitureFixturesAndOfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6939e8de-af07-4e38-afad-f0fe0937698f" xlink:to="loc_dsp_FurnitureFixturesAndOfficeEquipmentMember_51a9b4e5-5d00-453f-9f3f-3ad606cad8c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_74455375-f4e2-4f7c-80ce-646930e965ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6939e8de-af07-4e38-afad-f0fe0937698f" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_74455375-f4e2-4f7c-80ce-646930e965ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_26a55d4f-4962-44c4-9247-cb1350103f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d6120c89-a145-4172-aed5-c1722e8bd1f8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_26a55d4f-4962-44c4-9247-cb1350103f2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_a1eba3de-7006-4adf-b15e-70d6f6f13d6d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d6120c89-a145-4172-aed5-c1722e8bd1f8" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_a1eba3de-7006-4adf-b15e-70d6f6f13d6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_0c42caa2-ac00-40ec-8b11-08e8f65e7957" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d6120c89-a145-4172-aed5-c1722e8bd1f8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_0c42caa2-ac00-40ec-8b11-08e8f65e7957" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/PropertyEquipmentandSoftwareNetScheduleofDepreciationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#PropertyEquipmentandSoftwareNetScheduleofDepreciationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/PropertyEquipmentandSoftwareNetScheduleofDepreciationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4bf12e3a-efdc-4cbf-8097-819b6465e745" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fef59461-5e1f-4be6-bfd9-50661317777e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4bf12e3a-efdc-4cbf-8097-819b6465e745" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fef59461-5e1f-4be6-bfd9-50661317777e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_1338026c-d6c2-46c1-8e5b-29cf95197eb9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fef59461-5e1f-4be6-bfd9-50661317777e" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_1338026c-d6c2-46c1-8e5b-29cf95197eb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_1338026c-d6c2-46c1-8e5b-29cf95197eb9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_1338026c-d6c2-46c1-8e5b-29cf95197eb9" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_1338026c-d6c2-46c1-8e5b-29cf95197eb9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_219f6ffb-590c-4d09-beab-8385ed20b44b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_1338026c-d6c2-46c1-8e5b-29cf95197eb9" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_219f6ffb-590c-4d09-beab-8385ed20b44b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_PlatformOperationsMember_4ab5eb25-ea04-4552-b7ff-fb8ad59e524e" xlink:href="dsp-20240930.xsd#dsp_PlatformOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_219f6ffb-590c-4d09-beab-8385ed20b44b" xlink:to="loc_dsp_PlatformOperationsMember_4ab5eb25-ea04-4552-b7ff-fb8ad59e524e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_c7443574-da05-4bee-908c-de7809a939e6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_219f6ffb-590c-4d09-beab-8385ed20b44b" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_c7443574-da05-4bee-908c-de7809a939e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_TechnologyAndDevelopmentMember_c9deeb4b-b8f6-4603-9436-08361ecd693f" xlink:href="dsp-20240930.xsd#dsp_TechnologyAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_219f6ffb-590c-4d09-beab-8385ed20b44b" xlink:to="loc_dsp_TechnologyAndDevelopmentMember_c9deeb4b-b8f6-4603-9436-08361ecd693f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_55ec1dcd-5728-41c4-b557-9b3c00dcc70d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_219f6ffb-590c-4d09-beab-8385ed20b44b" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_55ec1dcd-5728-41c4-b557-9b3c00dcc70d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_e6400160-2733-49ea-8081-1b14fb6579bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4bf12e3a-efdc-4cbf-8097-819b6465e745" xlink:to="loc_us-gaap_Depreciation_e6400160-2733-49ea-8081-1b14fb6579bc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/LeasesAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#LeasesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/LeasesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_cb06b30f-ac71-4b36-9bc1-ebe1ba7b1c27" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_cb06b30f-ac71-4b36-9bc1-ebe1ba7b1c27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_6d3dbab8-4129-4838-8a56-ab1eb98ff8f1" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_cb06b30f-ac71-4b36-9bc1-ebe1ba7b1c27" xlink:to="loc_srt_RangeAxis_6d3dbab8-4129-4838-8a56-ab1eb98ff8f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6d3dbab8-4129-4838-8a56-ab1eb98ff8f1_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_6d3dbab8-4129-4838-8a56-ab1eb98ff8f1" xlink:to="loc_srt_RangeMember_6d3dbab8-4129-4838-8a56-ab1eb98ff8f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9b25dc5e-f7da-4dfc-b820-69fc7af4e1e3" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_6d3dbab8-4129-4838-8a56-ab1eb98ff8f1" xlink:to="loc_srt_RangeMember_9b25dc5e-f7da-4dfc-b820-69fc7af4e1e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fbd8f26f-53ce-4f3a-b1c8-0f0543c42c9c" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9b25dc5e-f7da-4dfc-b820-69fc7af4e1e3" xlink:to="loc_srt_MaximumMember_fbd8f26f-53ce-4f3a-b1c8-0f0543c42c9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_d57534b5-41b5-4b6b-93dd-38204a533505" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_d57534b5-41b5-4b6b-93dd-38204a533505" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_8b4ced9e-75fa-41bf-b8c1-77fa1942fa1e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_8b4ced9e-75fa-41bf-b8c1-77fa1942fa1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_e3b33e55-fb2e-4088-b679-ae6f271caea4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_e3b33e55-fb2e-4088-b679-ae6f271caea4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_OperatingLeaseWeightedAverageIncrementalBorrowingRate_1882558b-30fc-42f0-9d74-5fb0788c3a7c" xlink:href="dsp-20240930.xsd#dsp_OperatingLeaseWeightedAverageIncrementalBorrowingRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_dsp_OperatingLeaseWeightedAverageIncrementalBorrowingRate_1882558b-30fc-42f0-9d74-5fb0788c3a7c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_3ac20bcc-f215-4b74-ada7-88a53be1a560" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_us-gaap_OperatingLeasePayments_3ac20bcc-f215-4b74-ada7-88a53be1a560" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermLeaseCommitmentAmount_b6111bf6-f3ae-4088-9b1f-678d66996f7e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermLeaseCommitmentAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_us-gaap_ShortTermLeaseCommitmentAmount_b6111bf6-f3ae-4088-9b1f-678d66996f7e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_LesseeOperatingLeaseRemainingLeaseTermShortTermLeases_3a7f7905-d031-4507-a60b-467faf28ec6e" xlink:href="dsp-20240930.xsd#dsp_LesseeOperatingLeaseRemainingLeaseTermShortTermLeases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_dsp_LesseeOperatingLeaseRemainingLeaseTermShortTermLeases_3a7f7905-d031-4507-a60b-467faf28ec6e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ShortTermLeaseCumulativeDaysAvailableForUse_3ebb4af8-d3c9-4647-9a99-d2e433cb1c78" xlink:href="dsp-20240930.xsd#dsp_ShortTermLeaseCumulativeDaysAvailableForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_decb1003-e46b-4ccd-9504-776098c1478c" xlink:to="loc_dsp_ShortTermLeaseCumulativeDaysAvailableForUse_3ebb4af8-d3c9-4647-9a99-d2e433cb1c78" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/IntangibleAssetsNetSummaryofBalancesofIntangiblesAssetsandAccumulatedAmortizationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#IntangibleAssetsNetSummaryofBalancesofIntangiblesAssetsandAccumulatedAmortizationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/IntangibleAssetsNetSummaryofBalancesofIntangiblesAssetsandAccumulatedAmortizationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b0852ab-427a-4c2c-aa2b-26a8a396492f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_d7be92b9-2989-4fcf-97f1-e9bcdee92366" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b0852ab-427a-4c2c-aa2b-26a8a396492f" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_d7be92b9-2989-4fcf-97f1-e9bcdee92366" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0f6ca277-124d-404c-8a00-7d4ab60f1290" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_d7be92b9-2989-4fcf-97f1-e9bcdee92366" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0f6ca277-124d-404c-8a00-7d4ab60f1290" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_0f6ca277-124d-404c-8a00-7d4ab60f1290_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0f6ca277-124d-404c-8a00-7d4ab60f1290" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_0f6ca277-124d-404c-8a00-7d4ab60f1290_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_19b50c0d-898b-456b-95de-a9ca6543bca8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0f6ca277-124d-404c-8a00-7d4ab60f1290" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_19b50c0d-898b-456b-95de-a9ca6543bca8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_b79a984b-684e-4990-9bc7-1221754efd9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_19b50c0d-898b-456b-95de-a9ca6543bca8" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_b79a984b-684e-4990-9bc7-1221754efd9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_d0dfd067-1dac-4834-b71a-9212ec7e7068" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_19b50c0d-898b-456b-95de-a9ca6543bca8" xlink:to="loc_us-gaap_CustomerRelationshipsMember_d0dfd067-1dac-4834-b71a-9212ec7e7068" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_3e644372-ade0-40e4-abe1-633cdbc33dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_19b50c0d-898b-456b-95de-a9ca6543bca8" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_3e644372-ade0-40e4-abe1-633cdbc33dc4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_e0d0f51e-3e99-4833-ab17-4be17bfa109b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b0852ab-427a-4c2c-aa2b-26a8a396492f" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_e0d0f51e-3e99-4833-ab17-4be17bfa109b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_8262fd7d-0b4c-4953-ac21-b4100eedbfc3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b0852ab-427a-4c2c-aa2b-26a8a396492f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_8262fd7d-0b4c-4953-ac21-b4100eedbfc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_2d68571a-409d-4817-88b7-75be6d6dfd00" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b0852ab-427a-4c2c-aa2b-26a8a396492f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_2d68571a-409d-4817-88b7-75be6d6dfd00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_023ac3d1-0ffe-4340-bde7-5eb86aab2d71" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b0852ab-427a-4c2c-aa2b-26a8a396492f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_023ac3d1-0ffe-4340-bde7-5eb86aab2d71" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/IntangibleAssetsNetSummaryofAmortizationofIntangibleAssetsRecordedinConsolidatedStatementsofOperationsDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#IntangibleAssetsNetSummaryofAmortizationofIntangibleAssetsRecordedinConsolidatedStatementsofOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/IntangibleAssetsNetSummaryofAmortizationofIntangibleAssetsRecordedinConsolidatedStatementsofOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_5118cb06-1c37-40e1-a08f-ece68a8765e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_eb7296ff-4610-48c7-a5ff-f94ba5d4ee3d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_5118cb06-1c37-40e1-a08f-ece68a8765e3" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_eb7296ff-4610-48c7-a5ff-f94ba5d4ee3d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_014f8b2b-59a8-4386-a574-dcb90bfe4e6a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_eb7296ff-4610-48c7-a5ff-f94ba5d4ee3d" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_014f8b2b-59a8-4386-a574-dcb90bfe4e6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_014f8b2b-59a8-4386-a574-dcb90bfe4e6a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_014f8b2b-59a8-4386-a574-dcb90bfe4e6a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_014f8b2b-59a8-4386-a574-dcb90bfe4e6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_1fbfc954-0c92-4621-b03a-f86a58efb918" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_014f8b2b-59a8-4386-a574-dcb90bfe4e6a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_1fbfc954-0c92-4621-b03a-f86a58efb918" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_PlatformOperationsMember_610f12e1-8325-4e30-a2d5-5075d917ee15" xlink:href="dsp-20240930.xsd#dsp_PlatformOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_1fbfc954-0c92-4621-b03a-f86a58efb918" xlink:to="loc_dsp_PlatformOperationsMember_610f12e1-8325-4e30-a2d5-5075d917ee15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_d50cb5e9-6092-453c-a40e-4f1789475f98" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_1fbfc954-0c92-4621-b03a-f86a58efb918" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_d50cb5e9-6092-453c-a40e-4f1789475f98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_TechnologyAndDevelopmentMember_01f135e8-1b1b-43da-a78a-6ab970849af4" xlink:href="dsp-20240930.xsd#dsp_TechnologyAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_1fbfc954-0c92-4621-b03a-f86a58efb918" xlink:to="loc_dsp_TechnologyAndDevelopmentMember_01f135e8-1b1b-43da-a78a-6ab970849af4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_1b2c917e-60e4-4585-a42d-3fcfe414da42" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_1fbfc954-0c92-4621-b03a-f86a58efb918" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_1b2c917e-60e4-4585-a42d-3fcfe414da42" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_4692ad54-1f21-461f-88bd-ae9fcaa4e8b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_5118cb06-1c37-40e1-a08f-ece68a8765e3" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_4692ad54-1f21-461f-88bd-ae9fcaa4e8b1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/AccruedLiabilitiesAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#AccruedLiabilitiesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/AccruedLiabilitiesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_7a42c9a9-8dba-46b2-838a-34be5c61cadb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5f1aed7c-fa35-41f9-8bfa-b5ed0d99a7c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_7a42c9a9-8dba-46b2-838a-34be5c61cadb" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5f1aed7c-fa35-41f9-8bfa-b5ed0d99a7c6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9dece383-e3a4-43c7-8e49-60ab697a9561" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5f1aed7c-fa35-41f9-8bfa-b5ed0d99a7c6" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9dece383-e3a4-43c7-8e49-60ab697a9561" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_9dece383-e3a4-43c7-8e49-60ab697a9561_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9dece383-e3a4-43c7-8e49-60ab697a9561" xlink:to="loc_us-gaap_RelatedPartyDomain_9dece383-e3a4-43c7-8e49-60ab697a9561_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_3c492bb6-c093-4f4b-8af6-ef37e2b12914" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9dece383-e3a4-43c7-8e49-60ab697a9561" xlink:to="loc_us-gaap_RelatedPartyDomain_3c492bb6-c093-4f4b-8af6-ef37e2b12914" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_4cec28fe-04b4-4a3a-9068-d9c13862fc51" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_3c492bb6-c093-4f4b-8af6-ef37e2b12914" xlink:to="loc_srt_AffiliatedEntityMember_4cec28fe-04b4-4a3a-9068-d9c13862fc51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_b36e838e-c111-4454-b8c8-7d543b61d947" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_7a42c9a9-8dba-46b2-838a-34be5c61cadb" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_b36e838e-c111-4454-b8c8-7d543b61d947" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_2bfaeb0c-fce0-4522-bb98-2ece91ca3b28" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_7a42c9a9-8dba-46b2-838a-34be5c61cadb" xlink:to="loc_us-gaap_CostsAndExpenses_2bfaeb0c-fce0-4522-bb98-2ece91ca3b28" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/RevolvingCreditFacilityAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#RevolvingCreditFacilityAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/RevolvingCreditFacilityAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_c1ce5f0f-7616-47cd-bb91-dcfb97191b92" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_c1ce5f0f-7616-47cd-bb91-dcfb97191b92" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_2956f306-b738-4c81-9890-1989b61f503c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_c1ce5f0f-7616-47cd-bb91-dcfb97191b92" xlink:to="loc_us-gaap_CreditFacilityAxis_2956f306-b738-4c81-9890-1989b61f503c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_2956f306-b738-4c81-9890-1989b61f503c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_2956f306-b738-4c81-9890-1989b61f503c" xlink:to="loc_us-gaap_CreditFacilityDomain_2956f306-b738-4c81-9890-1989b61f503c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_2af33997-4256-402b-80ff-cdfa59727631" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_2956f306-b738-4c81-9890-1989b61f503c" xlink:to="loc_us-gaap_CreditFacilityDomain_2af33997-4256-402b-80ff-cdfa59727631" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_c00bd16c-acae-44ed-b7e8-d5bb2cc0a52c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_2af33997-4256-402b-80ff-cdfa59727631" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_c00bd16c-acae-44ed-b7e8-d5bb2cc0a52c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_dc942766-12c2-4c18-b684-49bccc5ff2bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_c1ce5f0f-7616-47cd-bb91-dcfb97191b92" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_dc942766-12c2-4c18-b684-49bccc5ff2bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_dc942766-12c2-4c18-b684-49bccc5ff2bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_dc942766-12c2-4c18-b684-49bccc5ff2bf" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_dc942766-12c2-4c18-b684-49bccc5ff2bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_cb786876-eebe-4c2c-a88f-afb49ff577ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_dc942766-12c2-4c18-b684-49bccc5ff2bf" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_cb786876-eebe-4c2c-a88f-afb49ff577ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_PNCBankMember_1c6fd6b8-8524-42e1-be35-576a048c3823" xlink:href="dsp-20240930.xsd#dsp_PNCBankMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_cb786876-eebe-4c2c-a88f-afb49ff577ec" xlink:to="loc_dsp_PNCBankMember_1c6fd6b8-8524-42e1-be35-576a048c3823" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_fbb17054-a307-4ada-ac3c-7221e876632c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_c1ce5f0f-7616-47cd-bb91-dcfb97191b92" xlink:to="loc_us-gaap_VariableRateAxis_fbb17054-a307-4ada-ac3c-7221e876632c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_fbb17054-a307-4ada-ac3c-7221e876632c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_fbb17054-a307-4ada-ac3c-7221e876632c" xlink:to="loc_us-gaap_VariableRateDomain_fbb17054-a307-4ada-ac3c-7221e876632c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_207535e1-0fc2-4345-bcbf-f5dc0dd3f575" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_fbb17054-a307-4ada-ac3c-7221e876632c" xlink:to="loc_us-gaap_VariableRateDomain_207535e1-0fc2-4345-bcbf-f5dc0dd3f575" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_b24bde43-722d-45ea-8b82-2b94189e513a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_207535e1-0fc2-4345-bcbf-f5dc0dd3f575" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_b24bde43-722d-45ea-8b82-2b94189e513a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_SecuredOvernightFinancingRateMember_62307875-1ad9-4835-95eb-b19db1505d04" xlink:href="dsp-20240930.xsd#dsp_SecuredOvernightFinancingRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_207535e1-0fc2-4345-bcbf-f5dc0dd3f575" xlink:to="loc_dsp_SecuredOvernightFinancingRateMember_62307875-1ad9-4835-95eb-b19db1505d04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_LondonInterbankOfferedRateLIBORSwapRate1Member_1255fc6e-2d65-4995-abf9-045552b980d4" xlink:href="dsp-20240930.xsd#dsp_LondonInterbankOfferedRateLIBORSwapRate1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_207535e1-0fc2-4345-bcbf-f5dc0dd3f575" xlink:to="loc_dsp_LondonInterbankOfferedRateLIBORSwapRate1Member_1255fc6e-2d65-4995-abf9-045552b980d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_9fa28340-0bc2-4a83-ab9a-f09e1e8966c7" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_c1ce5f0f-7616-47cd-bb91-dcfb97191b92" xlink:to="loc_srt_RangeAxis_9fa28340-0bc2-4a83-ab9a-f09e1e8966c7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9fa28340-0bc2-4a83-ab9a-f09e1e8966c7_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_9fa28340-0bc2-4a83-ab9a-f09e1e8966c7" xlink:to="loc_srt_RangeMember_9fa28340-0bc2-4a83-ab9a-f09e1e8966c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_826aab07-534a-4829-b8e3-cb0af8f271dc" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_9fa28340-0bc2-4a83-ab9a-f09e1e8966c7" xlink:to="loc_srt_RangeMember_826aab07-534a-4829-b8e3-cb0af8f271dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_2d57759e-35a5-4a83-a23c-4a403200f2f6" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_826aab07-534a-4829-b8e3-cb0af8f271dc" xlink:to="loc_srt_MinimumMember_2d57759e-35a5-4a83-a23c-4a403200f2f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_946f4193-b27b-495c-b63d-dfe6fe88d771" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_826aab07-534a-4829-b8e3-cb0af8f271dc" xlink:to="loc_srt_MaximumMember_946f4193-b27b-495c-b63d-dfe6fe88d771" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_2f6ecd49-8dc8-40eb-acc5-e89096d38a66" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_c1ce5f0f-7616-47cd-bb91-dcfb97191b92" xlink:to="loc_us-gaap_DebtInstrumentAxis_2f6ecd49-8dc8-40eb-acc5-e89096d38a66" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2f6ecd49-8dc8-40eb-acc5-e89096d38a66_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_2f6ecd49-8dc8-40eb-acc5-e89096d38a66" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2f6ecd49-8dc8-40eb-acc5-e89096d38a66_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_483459d9-eef2-4b05-8985-c711e3e723ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_2f6ecd49-8dc8-40eb-acc5-e89096d38a66" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_483459d9-eef2-4b05-8985-c711e3e723ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_LoanAgreementMember_e186b997-2688-4988-a2a7-f3b9134a0b23" xlink:href="dsp-20240930.xsd#dsp_LoanAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_483459d9-eef2-4b05-8985-c711e3e723ca" xlink:to="loc_dsp_LoanAgreementMember_e186b997-2688-4988-a2a7-f3b9134a0b23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_b0b7a243-8161-437c-b3b7-12c39ffae3e2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_b0b7a243-8161-437c-b3b7-12c39ffae3e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_5596dea9-3a14-416a-925c-ee37cdbf3d96" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_5596dea9-3a14-416a-925c-ee37cdbf3d96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_2c7780f0-6677-4828-900b-8b7e5781d430" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:to="loc_us-gaap_LineOfCredit_2c7780f0-6677-4828-900b-8b7e5781d430" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_f2538417-f1e2-4005-8ec3-32facdc03d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_f2538417-f1e2-4005-8ec3-32facdc03d4c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_LineOfCreditFacilityFixedCoverageChargeRatio_6a9facef-4def-49b3-bfe7-c5885df238db" xlink:href="dsp-20240930.xsd#dsp_LineOfCreditFacilityFixedCoverageChargeRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:to="loc_dsp_LineOfCreditFacilityFixedCoverageChargeRatio_6a9facef-4def-49b3-bfe7-c5885df238db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_LineOfCreditFacilityUndrawnAvailabilityPercentage_b4c6b2b3-13de-4721-8749-b5055ce1dd85" xlink:href="dsp-20240930.xsd#dsp_LineOfCreditFacilityUndrawnAvailabilityPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_61d2ad5f-8c29-4564-aa2b-91403c013e9c" xlink:to="loc_dsp_LineOfCreditFacilityUndrawnAvailabilityPercentage_b4c6b2b3-13de-4721-8749-b5055ce1dd85" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#StockBasedCompensationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_371e66f9-21a6-4f13-8294-4d2ff05772d1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_371e66f9-21a6-4f13-8294-4d2ff05772d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_0693e613-0de5-4bfd-bfd9-92d198bd54aa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_371e66f9-21a6-4f13-8294-4d2ff05772d1" xlink:to="loc_us-gaap_PlanNameAxis_0693e613-0de5-4bfd-bfd9-92d198bd54aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_0693e613-0de5-4bfd-bfd9-92d198bd54aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_0693e613-0de5-4bfd-bfd9-92d198bd54aa" xlink:to="loc_us-gaap_PlanNameDomain_0693e613-0de5-4bfd-bfd9-92d198bd54aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_486b4bb0-e3cd-4417-be41-1e6b329d1de9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_0693e613-0de5-4bfd-bfd9-92d198bd54aa" xlink:to="loc_us-gaap_PlanNameDomain_486b4bb0-e3cd-4417-be41-1e6b329d1de9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_LongTermIncentivePlanMember_b3bab1eb-9669-41a2-880c-b5e844bb7a68" xlink:href="dsp-20240930.xsd#dsp_LongTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_486b4bb0-e3cd-4417-be41-1e6b329d1de9" xlink:to="loc_dsp_LongTermIncentivePlanMember_b3bab1eb-9669-41a2-880c-b5e844bb7a68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_9349d338-3d09-4cbd-996c-19cf3ffc36d2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_371e66f9-21a6-4f13-8294-4d2ff05772d1" xlink:to="loc_us-gaap_AwardTypeAxis_9349d338-3d09-4cbd-996c-19cf3ffc36d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9349d338-3d09-4cbd-996c-19cf3ffc36d2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_9349d338-3d09-4cbd-996c-19cf3ffc36d2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9349d338-3d09-4cbd-996c-19cf3ffc36d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_eba465b7-9829-4613-81f4-1e5a8a04906c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_9349d338-3d09-4cbd-996c-19cf3ffc36d2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_eba465b7-9829-4613-81f4-1e5a8a04906c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_1159f124-e36d-47ea-ba17-dfae6afcda48" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_eba465b7-9829-4613-81f4-1e5a8a04906c" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_1159f124-e36d-47ea-ba17-dfae6afcda48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_NonqualifiedStockOptionsMember_69842a31-a559-42c5-99e3-3270835aea42" xlink:href="dsp-20240930.xsd#dsp_NonqualifiedStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_eba465b7-9829-4613-81f4-1e5a8a04906c" xlink:to="loc_dsp_NonqualifiedStockOptionsMember_69842a31-a559-42c5-99e3-3270835aea42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_8ccb3049-c36c-4ff9-a2f0-780834f68da2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_371e66f9-21a6-4f13-8294-4d2ff05772d1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_8ccb3049-c36c-4ff9-a2f0-780834f68da2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_8ccb3049-c36c-4ff9-a2f0-780834f68da2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8ccb3049-c36c-4ff9-a2f0-780834f68da2" xlink:to="loc_us-gaap_ClassOfStockDomain_8ccb3049-c36c-4ff9-a2f0-780834f68da2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_846b8bf9-3fe4-42be-9cae-bcba778433ef" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8ccb3049-c36c-4ff9-a2f0-780834f68da2" xlink:to="loc_us-gaap_ClassOfStockDomain_846b8bf9-3fe4-42be-9cae-bcba778433ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_6b311918-a063-45ab-ae3f-97432f6bd029" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_846b8bf9-3fe4-42be-9cae-bcba778433ef" xlink:to="loc_us-gaap_CommonClassAMember_6b311918-a063-45ab-ae3f-97432f6bd029" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_37666625-9da0-463c-b159-27bd99b83597" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_37666625-9da0-463c-b159-27bd99b83597" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_df666fc3-6897-4a58-a168-a60153a4a809" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_df666fc3-6897-4a58-a168-a60153a4a809" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_b5ea4aea-87ae-4975-af44-ace760e2137f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_b5ea4aea-87ae-4975-af44-ace760e2137f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_b8e8358d-45e1-4151-b701-7072e8fba4bd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_b8e8358d-45e1-4151-b701-7072e8fba4bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_1fd7a9c3-fbf7-4313-934e-b4c64148e8bb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_1fd7a9c3-fbf7-4313-934e-b4c64148e8bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_aa769998-4e3c-4152-9a51-68a10f4e133f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2f43619c-f8d5-4a65-928e-8b49e70d6d54" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_aa769998-4e3c-4152-9a51-68a10f4e133f" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/StockBasedCompensationSummaryofStockbasedCompensationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#StockBasedCompensationSummaryofStockbasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/StockBasedCompensationSummaryofStockbasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_33ffb1ff-9bb2-45ff-9ace-1ed0fe9f46ea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_3fa143b0-8ec1-4934-ac63-933bcedf4288" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_33ffb1ff-9bb2-45ff-9ace-1ed0fe9f46ea" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_3fa143b0-8ec1-4934-ac63-933bcedf4288" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_c2b157f9-0073-4746-95fb-37b6ccd81439" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_3fa143b0-8ec1-4934-ac63-933bcedf4288" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_c2b157f9-0073-4746-95fb-37b6ccd81439" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_c2b157f9-0073-4746-95fb-37b6ccd81439_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_c2b157f9-0073-4746-95fb-37b6ccd81439" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_c2b157f9-0073-4746-95fb-37b6ccd81439_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_26baed23-e773-4bae-9616-f5df47751dd7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_c2b157f9-0073-4746-95fb-37b6ccd81439" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_26baed23-e773-4bae-9616-f5df47751dd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_PlatformOperationsMember_06e4b6d6-7c81-426d-abbf-f6510207ab7d" xlink:href="dsp-20240930.xsd#dsp_PlatformOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_26baed23-e773-4bae-9616-f5df47751dd7" xlink:to="loc_dsp_PlatformOperationsMember_06e4b6d6-7c81-426d-abbf-f6510207ab7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_257d21cf-2f95-4ac9-9eb1-8f4cc659c5d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_26baed23-e773-4bae-9616-f5df47751dd7" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_257d21cf-2f95-4ac9-9eb1-8f4cc659c5d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_TechnologyAndDevelopmentMember_38a7ee58-3f5c-4467-b6ce-10a40cbaf31e" xlink:href="dsp-20240930.xsd#dsp_TechnologyAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_26baed23-e773-4bae-9616-f5df47751dd7" xlink:to="loc_dsp_TechnologyAndDevelopmentMember_38a7ee58-3f5c-4467-b6ce-10a40cbaf31e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_ab99ea58-16db-43e1-ac5a-e4e09ee9d429" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_26baed23-e773-4bae-9616-f5df47751dd7" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_ab99ea58-16db-43e1-ac5a-e4e09ee9d429" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_7b621377-ddc0-4d31-8d8d-c235665879c0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_33ffb1ff-9bb2-45ff-9ace-1ed0fe9f46ea" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_7b621377-ddc0-4d31-8d8d-c235665879c0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/StockBasedCompensationSummaryofRSUActivityDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#StockBasedCompensationSummaryofRSUActivityDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/StockBasedCompensationSummaryofRSUActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_51d3b5c7-26c9-4755-89a3-8f3ee5aa9e3e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a45fa3ec-0822-404e-9ff7-5e7506a219c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_51d3b5c7-26c9-4755-89a3-8f3ee5aa9e3e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a45fa3ec-0822-404e-9ff7-5e7506a219c6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_55f8e348-04fd-404e-b938-fc75a5508de7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a45fa3ec-0822-404e-9ff7-5e7506a219c6" xlink:to="loc_us-gaap_AwardTypeAxis_55f8e348-04fd-404e-b938-fc75a5508de7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_55f8e348-04fd-404e-b938-fc75a5508de7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_55f8e348-04fd-404e-b938-fc75a5508de7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_55f8e348-04fd-404e-b938-fc75a5508de7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dd5fa4f3-21cd-4ab1-9341-726f33f13144" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_55f8e348-04fd-404e-b938-fc75a5508de7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dd5fa4f3-21cd-4ab1-9341-726f33f13144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_4d230204-431a-472b-8b53-6abf279d3a8d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dd5fa4f3-21cd-4ab1-9341-726f33f13144" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_4d230204-431a-472b-8b53-6abf279d3a8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_254db243-9bd9-41f2-9104-3c451f412710" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_51d3b5c7-26c9-4755-89a3-8f3ee5aa9e3e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_254db243-9bd9-41f2-9104-3c451f412710" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6dea366f-5296-44e3-9877-49d6f501f29f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_254db243-9bd9-41f2-9104-3c451f412710" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6dea366f-5296-44e3-9877-49d6f501f29f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_da3db218-a900-4859-9fb1-9bd262e4c670" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_254db243-9bd9-41f2-9104-3c451f412710" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_da3db218-a900-4859-9fb1-9bd262e4c670" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_bc37d985-1379-4fe5-83dd-2086a408ca38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_254db243-9bd9-41f2-9104-3c451f412710" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_bc37d985-1379-4fe5-83dd-2086a408ca38" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_aef1cf82-6383-4188-947b-1ee18e1a7519" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_254db243-9bd9-41f2-9104-3c451f412710" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_aef1cf82-6383-4188-947b-1ee18e1a7519" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_8022512e-a22e-4be0-8c99-2c0c5ed96b13" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd890f0a-ff42-4716-a054-b92dd0e48492" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_51d3b5c7-26c9-4755-89a3-8f3ee5aa9e3e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd890f0a-ff42-4716-a054-b92dd0e48492" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_8e36edda-b748-45f8-8a2a-6ff0f9ccd667" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd890f0a-ff42-4716-a054-b92dd0e48492" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_8e36edda-b748-45f8-8a2a-6ff0f9ccd667" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_56ae7b44-63b9-4b87-af9a-2703e8032947" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd890f0a-ff42-4716-a054-b92dd0e48492" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_56ae7b44-63b9-4b87-af9a-2703e8032947" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_402288a5-3bb1-47be-84fa-664d35e2ac16" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd890f0a-ff42-4716-a054-b92dd0e48492" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_402288a5-3bb1-47be-84fa-664d35e2ac16" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_dc38c8f8-cc16-4e6a-b211-ff0d51a417b6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd890f0a-ff42-4716-a054-b92dd0e48492" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_dc38c8f8-cc16-4e6a-b211-ff0d51a417b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_f515a398-97cd-4baa-9cec-42835ed45044" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/StockBasedCompensationSummaryofNonqualifiedStockOptionActivityDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#StockBasedCompensationSummaryofNonqualifiedStockOptionActivityDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/StockBasedCompensationSummaryofNonqualifiedStockOptionActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dfe2cd1c-7f12-4204-936c-06d06eed0165" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dfe2cd1c-7f12-4204-936c-06d06eed0165" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_cb37993a-ccd5-4750-a297-856edf698e25" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dfe2cd1c-7f12-4204-936c-06d06eed0165" xlink:to="loc_us-gaap_AwardTypeAxis_cb37993a-ccd5-4750-a297-856edf698e25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cb37993a-ccd5-4750-a297-856edf698e25_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_cb37993a-ccd5-4750-a297-856edf698e25" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cb37993a-ccd5-4750-a297-856edf698e25_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8a3a064-a2f1-4f8f-98fd-f2d4af93ff37" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_cb37993a-ccd5-4750-a297-856edf698e25" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8a3a064-a2f1-4f8f-98fd-f2d4af93ff37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_NonqualifiedStockOptionsMember_7457b06b-4feb-489f-a1e7-c7164c06967e" xlink:href="dsp-20240930.xsd#dsp_NonqualifiedStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8a3a064-a2f1-4f8f-98fd-f2d4af93ff37" xlink:to="loc_dsp_NonqualifiedStockOptionsMember_7457b06b-4feb-489f-a1e7-c7164c06967e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_6451076f-8825-4938-8bb4-de9b8e21ab0c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_6451076f-8825-4938-8bb4-de9b8e21ab0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_0a375a0f-03e4-4fab-9d1b-45e531a24f5d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_6451076f-8825-4938-8bb4-de9b8e21ab0c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_0a375a0f-03e4-4fab-9d1b-45e531a24f5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c9fcaa16-be40-42cf-a98f-444deebd4950" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_6451076f-8825-4938-8bb4-de9b8e21ab0c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c9fcaa16-be40-42cf-a98f-444deebd4950" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_b0f39dd8-915e-41d2-820b-8414aa01e2ef" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_6451076f-8825-4938-8bb4-de9b8e21ab0c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_b0f39dd8-915e-41d2-820b-8414aa01e2ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_fb92fa32-7f28-417b-988e-58477ed9c041" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_6451076f-8825-4938-8bb4-de9b8e21ab0c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_fb92fa32-7f28-417b-988e-58477ed9c041" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_d60ce37c-0608-47f3-9086-c5aa6df15d16" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_6451076f-8825-4938-8bb4-de9b8e21ab0c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_d60ce37c-0608-47f3-9086-c5aa6df15d16" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_f00f5ca0-b120-4057-80cb-1da5db68d113" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableNumberOfShares_55b9548d-74b2-40f3-91f9-a624522cb13c" xlink:href="dsp-20240930.xsd#dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableNumberOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableNumberOfShares_55b9548d-74b2-40f3-91f9-a624522cb13c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_2a573022-f292-4f0e-a690-e7ea1cbe94ff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_2a573022-f292-4f0e-a690-e7ea1cbe94ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_7fdde9be-0abd-4095-90f8-6dc9160330ab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_2a573022-f292-4f0e-a690-e7ea1cbe94ff" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_7fdde9be-0abd-4095-90f8-6dc9160330ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_91ea271d-d2ce-4ced-87a6-3200a7af72c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_2a573022-f292-4f0e-a690-e7ea1cbe94ff" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_91ea271d-d2ce-4ced-87a6-3200a7af72c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_aef95360-adf5-4fda-874e-1bf25fe663d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_2a573022-f292-4f0e-a690-e7ea1cbe94ff" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_aef95360-adf5-4fda-874e-1bf25fe663d4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_fda93ad0-8168-4282-aa1c-f19b8b919182" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_2a573022-f292-4f0e-a690-e7ea1cbe94ff" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_fda93ad0-8168-4282-aa1c-f19b8b919182" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_dedf0f02-109f-4988-a1c0-fc909de9e475" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_2a573022-f292-4f0e-a690-e7ea1cbe94ff" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_dedf0f02-109f-4988-a1c0-fc909de9e475" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_5a491d1e-e307-4339-b4ab-ce578e26b6b7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableWeightedAverageExercisePrice_c5d2cf61-40d3-4fb8-8190-0754d2eae9a4" xlink:href="dsp-20240930.xsd#dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableWeightedAverageExercisePrice_c5d2cf61-40d3-4fb8-8190-0754d2eae9a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract_41f77d37-082a-44eb-b7bd-37115d873cd0" xlink:href="dsp-20240930.xsd#dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract_41f77d37-082a-44eb-b7bd-37115d873cd0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_cfaa0941-6fb8-4a8e-8358-33ac3998be5e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract_41f77d37-082a-44eb-b7bd-37115d873cd0" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_cfaa0941-6fb8-4a8e-8358-33ac3998be5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableWeightedAverageRemainingContractualTerm_29c64519-2e30-4d30-a727-3afe7006262e" xlink:href="dsp-20240930.xsd#dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableWeightedAverageRemainingContractualTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTermAbstract_41f77d37-082a-44eb-b7bd-37115d873cd0" xlink:to="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExercisableWeightedAverageRemainingContractualTerm_29c64519-2e30-4d30-a727-3afe7006262e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_3a7ceb70-ea0d-424c-96a6-7c3f4ea7eb69" xlink:href="dsp-20240930.xsd#dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_3a7ceb70-ea0d-424c-96a6-7c3f4ea7eb69" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_b4beddc5-77b9-4aa0-b459-273c109c3b9a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_3a7ceb70-ea0d-424c-96a6-7c3f4ea7eb69" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_b4beddc5-77b9-4aa0-b459-273c109c3b9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_5ca9e40a-867e-434b-88a3-ba131f54da6f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d3b0e295-2db4-4e82-8d07-7ddb50ea1061" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_5ca9e40a-867e-434b-88a3-ba131f54da6f" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/StockBasedCompensationSummaryofAssumptionsusedinBlackScholesModeltoDetermineFairValueofNonqualifiedStockOptionsGrantedDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#StockBasedCompensationSummaryofAssumptionsusedinBlackScholesModeltoDetermineFairValueofNonqualifiedStockOptionsGrantedDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/StockBasedCompensationSummaryofAssumptionsusedinBlackScholesModeltoDetermineFairValueofNonqualifiedStockOptionsGrantedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_027f621b-5a9e-45e4-b9cb-ea1a01d23986" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_27fc9705-52f3-4b80-9ca7-2520279c5622" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_027f621b-5a9e-45e4-b9cb-ea1a01d23986" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_27fc9705-52f3-4b80-9ca7-2520279c5622" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_f4527b6b-b614-4a0a-b42e-4f7f0c4b2271" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_27fc9705-52f3-4b80-9ca7-2520279c5622" xlink:to="loc_srt_RangeAxis_f4527b6b-b614-4a0a-b42e-4f7f0c4b2271" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f4527b6b-b614-4a0a-b42e-4f7f0c4b2271_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_f4527b6b-b614-4a0a-b42e-4f7f0c4b2271" xlink:to="loc_srt_RangeMember_f4527b6b-b614-4a0a-b42e-4f7f0c4b2271_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f61a9568-0202-49ac-83b5-cb7235521c4a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_f4527b6b-b614-4a0a-b42e-4f7f0c4b2271" xlink:to="loc_srt_RangeMember_f61a9568-0202-49ac-83b5-cb7235521c4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_06af434d-11b2-461f-8d2d-ae4c908fe1f1" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f61a9568-0202-49ac-83b5-cb7235521c4a" xlink:to="loc_srt_MinimumMember_06af434d-11b2-461f-8d2d-ae4c908fe1f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_f399ecfa-75fc-47c3-b3df-54e09a88c991" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f61a9568-0202-49ac-83b5-cb7235521c4a" xlink:to="loc_srt_MaximumMember_f399ecfa-75fc-47c3-b3df-54e09a88c991" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_11bddfb0-6f9e-441f-b842-a894dfac25b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_027f621b-5a9e-45e4-b9cb-ea1a01d23986" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_11bddfb0-6f9e-441f-b842-a894dfac25b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_0661a8a3-638c-4f7c-b558-fde579901dd3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_027f621b-5a9e-45e4-b9cb-ea1a01d23986" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_0661a8a3-638c-4f7c-b558-fde579901dd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_671ca25b-09f8-43cb-8c28-4236b719d875" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_027f621b-5a9e-45e4-b9cb-ea1a01d23986" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_671ca25b-09f8-43cb-8c28-4236b719d875" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_7dc8fa34-796c-494c-b819-2944e9be05a6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_027f621b-5a9e-45e4-b9cb-ea1a01d23986" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_7dc8fa34-796c-494c-b819-2944e9be05a6" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/StockBasedCompensationSummaryofStockRepurchaseProgramDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#StockBasedCompensationSummaryofStockRepurchaseProgramDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/StockBasedCompensationSummaryofStockRepurchaseProgramDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d495ca34-f0ba-493e-95d9-71577525b837" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c668700b-c9ea-4cb5-8284-388ae516faff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d495ca34-f0ba-493e-95d9-71577525b837" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c668700b-c9ea-4cb5-8284-388ae516faff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_bc1e84f0-ec7f-462a-aa43-d74cc29223b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c668700b-c9ea-4cb5-8284-388ae516faff" xlink:to="loc_us-gaap_StatementClassOfStockAxis_bc1e84f0-ec7f-462a-aa43-d74cc29223b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_bc1e84f0-ec7f-462a-aa43-d74cc29223b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_bc1e84f0-ec7f-462a-aa43-d74cc29223b2" xlink:to="loc_us-gaap_ClassOfStockDomain_bc1e84f0-ec7f-462a-aa43-d74cc29223b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ca2e69fa-c5cd-427b-a85e-e60ef0e74bbc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_bc1e84f0-ec7f-462a-aa43-d74cc29223b2" xlink:to="loc_us-gaap_ClassOfStockDomain_ca2e69fa-c5cd-427b-a85e-e60ef0e74bbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_8842fe57-6046-4fcb-a15f-073220c72183" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ca2e69fa-c5cd-427b-a85e-e60ef0e74bbc" xlink:to="loc_us-gaap_CommonClassAMember_8842fe57-6046-4fcb-a15f-073220c72183" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_12d990c3-debb-47f2-bde6-73c938b9a567" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ca2e69fa-c5cd-427b-a85e-e60ef0e74bbc" xlink:to="loc_us-gaap_CommonClassBMember_12d990c3-debb-47f2-bde6-73c938b9a567" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_515dadc5-2fab-42f8-9ba9-4e12a1758340" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d495ca34-f0ba-493e-95d9-71577525b837" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_515dadc5-2fab-42f8-9ba9-4e12a1758340" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_0ea9ce54-2cf3-4d95-96a0-3450ce418727" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d495ca34-f0ba-493e-95d9-71577525b837" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_0ea9ce54-2cf3-4d95-96a0-3450ce418727" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/LossPerShareCalculationofBasicandDilutedNetLossPerShareDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#LossPerShareCalculationofBasicandDilutedNetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/LossPerShareCalculationofBasicandDilutedNetLossPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_1c363396-554b-49f6-a744-c03afbfe01d8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_d81327c7-1f9d-462e-a50d-d6cb9693e74a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_1c363396-554b-49f6-a744-c03afbfe01d8" xlink:to="loc_us-gaap_StatementTable_d81327c7-1f9d-462e-a50d-d6cb9693e74a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_83b64a39-9d9f-4d39-b2a6-03809a337528" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d81327c7-1f9d-462e-a50d-d6cb9693e74a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_83b64a39-9d9f-4d39-b2a6-03809a337528" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_83b64a39-9d9f-4d39-b2a6-03809a337528_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_83b64a39-9d9f-4d39-b2a6-03809a337528" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_83b64a39-9d9f-4d39-b2a6-03809a337528_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_00a1b56b-4a87-4c7c-bd07-3c80ba19fddb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_83b64a39-9d9f-4d39-b2a6-03809a337528" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_00a1b56b-4a87-4c7c-bd07-3c80ba19fddb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_154fec09-d1c7-48f0-834f-4df4b5b45a86" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_00a1b56b-4a87-4c7c-bd07-3c80ba19fddb" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_154fec09-d1c7-48f0-834f-4df4b5b45a86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_NonqualifiedStockOptionsMember_41ee055c-ff20-4fd9-ac1c-1f9cb1f94c26" xlink:href="dsp-20240930.xsd#dsp_NonqualifiedStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_00a1b56b-4a87-4c7c-bd07-3c80ba19fddb" xlink:to="loc_dsp_NonqualifiedStockOptionsMember_41ee055c-ff20-4fd9-ac1c-1f9cb1f94c26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_85db5c90-9357-4dc6-aaae-ea6c99e8e0b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d81327c7-1f9d-462e-a50d-d6cb9693e74a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_85db5c90-9357-4dc6-aaae-ea6c99e8e0b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_85db5c90-9357-4dc6-aaae-ea6c99e8e0b1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_85db5c90-9357-4dc6-aaae-ea6c99e8e0b1" xlink:to="loc_us-gaap_ClassOfStockDomain_85db5c90-9357-4dc6-aaae-ea6c99e8e0b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_f611fbf0-d91b-4c4c-ac9e-931cb9fd42a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_85db5c90-9357-4dc6-aaae-ea6c99e8e0b1" xlink:to="loc_us-gaap_ClassOfStockDomain_f611fbf0-d91b-4c4c-ac9e-931cb9fd42a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_1dfaab1f-f781-4272-bd50-d39f4e91fdd7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_f611fbf0-d91b-4c4c-ac9e-931cb9fd42a2" xlink:to="loc_us-gaap_CommonClassAMember_1dfaab1f-f781-4272-bd50-d39f4e91fdd7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_3a6cf2a0-4a5a-4fef-a059-6e99b8025cd8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_f611fbf0-d91b-4c4c-ac9e-931cb9fd42a2" xlink:to="loc_us-gaap_CommonClassBMember_3a6cf2a0-4a5a-4fef-a059-6e99b8025cd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1c363396-554b-49f6-a744-c03afbfe01d8" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_a5865d8b-1ccc-4c1a-98d8-521affa31be0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:to="loc_us-gaap_ProfitLoss_a5865d8b-1ccc-4c1a-98d8-521affa31be0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_2b60166c-eb75-425b-a386-b4afa5228b2b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_2b60166c-eb75-425b-a386-b4afa5228b2b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_9aadad27-f54d-49ec-837c-db4bd75ac445" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_9aadad27-f54d-49ec-837c-db4bd75ac445" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmountOfDilutiveSecuritiesESOPConvertiblePreferredStock_af1230c3-05ed-46cd-b206-5c267dc6b0ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmountOfDilutiveSecuritiesESOPConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:to="loc_us-gaap_AmountOfDilutiveSecuritiesESOPConvertiblePreferredStock_af1230c3-05ed-46cd-b206-5c267dc6b0ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_DilutiveSecuritiesEffectOnBasicEarningsPerShareESOPConvertiblePreferredStockIncomeTaxEffect_62838bca-73f6-4a0a-97f4-a2fc245e3b05" xlink:href="dsp-20240930.xsd#dsp_DilutiveSecuritiesEffectOnBasicEarningsPerShareESOPConvertiblePreferredStockIncomeTaxEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:to="loc_dsp_DilutiveSecuritiesEffectOnBasicEarningsPerShareESOPConvertiblePreferredStockIncomeTaxEffect_62838bca-73f6-4a0a-97f4-a2fc245e3b05" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToParentDiluted_de479aff-83d3-4f72-b0fe-0b3a5c53a330" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAttributableToParentDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_4d52f908-5cdd-45a7-986e-b29a07b77e9c" xlink:to="loc_us-gaap_NetIncomeLossAttributableToParentDiluted_de479aff-83d3-4f72-b0fe-0b3a5c53a330" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_46116ef4-85c0-4530-93c6-fcb84eed342e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1c363396-554b-49f6-a744-c03afbfe01d8" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_46116ef4-85c0-4530-93c6-fcb84eed342e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_3e2d5bec-0bd0-4f5b-8e1a-016054f47ea7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_46116ef4-85c0-4530-93c6-fcb84eed342e" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_3e2d5bec-0bd0-4f5b-8e1a-016054f47ea7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_98142df9-5863-4ac6-a348-b73f66175b29" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_46116ef4-85c0-4530-93c6-fcb84eed342e" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_98142df9-5863-4ac6-a348-b73f66175b29" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_29983296-118c-44a8-b88a-1673e6320c9d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_46116ef4-85c0-4530-93c6-fcb84eed342e" xlink:to="loc_us-gaap_EarningsPerShareBasic_29983296-118c-44a8-b88a-1673e6320c9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_8c117204-9ace-4136-a2ba-ed475766b0f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_46116ef4-85c0-4530-93c6-fcb84eed342e" xlink:to="loc_us-gaap_EarningsPerShareDiluted_8c117204-9ace-4136-a2ba-ed475766b0f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_AntidilutiveSecuritiesExcludedFromEarningsLossPerShareAbstract_5f88ee57-8e41-4104-ae8b-b2b2b92f8b67" xlink:href="dsp-20240930.xsd#dsp_AntidilutiveSecuritiesExcludedFromEarningsLossPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1c363396-554b-49f6-a744-c03afbfe01d8" xlink:to="loc_dsp_AntidilutiveSecuritiesExcludedFromEarningsLossPerShareAbstract_5f88ee57-8e41-4104-ae8b-b2b2b92f8b67" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_67883590-8af4-49c8-bde8-dc01d8d7b61d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dsp_AntidilutiveSecuritiesExcludedFromEarningsLossPerShareAbstract_5f88ee57-8e41-4104-ae8b-b2b2b92f8b67" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_67883590-8af4-49c8-bde8-dc01d8d7b61d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/NoncontrollingInterestsAdditionalInformationDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#NoncontrollingInterestsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/NoncontrollingInterestsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestLineItems_b6c2691d-616a-447d-928b-240d338622a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestTable_b28d7883-c72c-443d-b88d-0ee99db6f2f3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MinorityInterestLineItems_b6c2691d-616a-447d-928b-240d338622a4" xlink:to="loc_us-gaap_MinorityInterestTable_b28d7883-c72c-443d-b88d-0ee99db6f2f3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_604c42fa-d8e5-4f18-99ae-9bef2c944313" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_b28d7883-c72c-443d-b88d-0ee99db6f2f3" xlink:to="loc_us-gaap_StatementClassOfStockAxis_604c42fa-d8e5-4f18-99ae-9bef2c944313" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_604c42fa-d8e5-4f18-99ae-9bef2c944313_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_604c42fa-d8e5-4f18-99ae-9bef2c944313" xlink:to="loc_us-gaap_ClassOfStockDomain_604c42fa-d8e5-4f18-99ae-9bef2c944313_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a1f561aa-cbb7-4ad3-8036-ea631e7cbf59" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_604c42fa-d8e5-4f18-99ae-9bef2c944313" xlink:to="loc_us-gaap_ClassOfStockDomain_a1f561aa-cbb7-4ad3-8036-ea631e7cbf59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_d9bbb6f5-1cb0-4785-9b55-ad4964dd944b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a1f561aa-cbb7-4ad3-8036-ea631e7cbf59" xlink:to="loc_us-gaap_CommonClassAMember_d9bbb6f5-1cb0-4785-9b55-ad4964dd944b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_MembersEquityClassBUnitsMember_e3770eab-ed54-46a3-a025-0cd07ca4c0c5" xlink:href="dsp-20240930.xsd#dsp_MembersEquityClassBUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a1f561aa-cbb7-4ad3-8036-ea631e7cbf59" xlink:to="loc_dsp_MembersEquityClassBUnitsMember_e3770eab-ed54-46a3-a025-0cd07ca4c0c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ExchangeUnitsForSharesOfCommonStock_c4f6e44e-b26e-4193-a135-3acb2c264af1" xlink:href="dsp-20240930.xsd#dsp_ExchangeUnitsForSharesOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_b6c2691d-616a-447d-928b-240d338622a4" xlink:to="loc_dsp_ExchangeUnitsForSharesOfCommonStock_c4f6e44e-b26e-4193-a135-3acb2c264af1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/NoncontrollingInterestsSummaryOwnershipofViantTechnologyLLCDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#NoncontrollingInterestsSummaryOwnershipofViantTechnologyLLCDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/NoncontrollingInterestsSummaryOwnershipofViantTechnologyLLCDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestLineItems_1037d8e8-9b48-44f5-8b96-4b77b6c0ade8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestTable_185237a7-fc08-43cb-9e03-178714b0aeb0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MinorityInterestLineItems_1037d8e8-9b48-44f5-8b96-4b77b6c0ade8" xlink:to="loc_us-gaap_MinorityInterestTable_185237a7-fc08-43cb-9e03-178714b0aeb0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_625f88e9-8328-49c6-9e72-d5d2228d2df8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_185237a7-fc08-43cb-9e03-178714b0aeb0" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_625f88e9-8328-49c6-9e72-d5d2228d2df8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_625f88e9-8328-49c6-9e72-d5d2228d2df8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_625f88e9-8328-49c6-9e72-d5d2228d2df8" xlink:to="loc_us-gaap_EquityComponentDomain_625f88e9-8328-49c6-9e72-d5d2228d2df8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_df96645d-b311-4b59-89d9-55c2ed6ea92d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_625f88e9-8328-49c6-9e72-d5d2228d2df8" xlink:to="loc_us-gaap_EquityComponentDomain_df96645d-b311-4b59-89d9-55c2ed6ea92d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_cdd21020-b173-4859-bbcd-feccc41792c4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_df96645d-b311-4b59-89d9-55c2ed6ea92d" xlink:to="loc_us-gaap_NoncontrollingInterestMember_cdd21020-b173-4859-bbcd-feccc41792c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_f530892b-5e79-4adf-a821-b6a8ab51bc9c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_185237a7-fc08-43cb-9e03-178714b0aeb0" xlink:to="loc_dei_LegalEntityAxis_f530892b-5e79-4adf-a821-b6a8ab51bc9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f530892b-5e79-4adf-a821-b6a8ab51bc9c_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_f530892b-5e79-4adf-a821-b6a8ab51bc9c" xlink:to="loc_dei_EntityDomain_f530892b-5e79-4adf-a821-b6a8ab51bc9c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_30243f17-ef3f-4f35-83d2-8556c7f996e6" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_f530892b-5e79-4adf-a821-b6a8ab51bc9c" xlink:to="loc_dei_EntityDomain_30243f17-ef3f-4f35-83d2-8556c7f996e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ViantTechnologyIncMember_4c66e62e-e6e2-4209-a38d-d3465781778f" xlink:href="dsp-20240930.xsd#dsp_ViantTechnologyIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_30243f17-ef3f-4f35-83d2-8556c7f996e6" xlink:to="loc_dsp_ViantTechnologyIncMember_4c66e62e-e6e2-4209-a38d-d3465781778f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_088c8274-f955-42b2-8581-9180712a3c78" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_185237a7-fc08-43cb-9e03-178714b0aeb0" xlink:to="loc_srt_OwnershipAxis_088c8274-f955-42b2-8581-9180712a3c78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_088c8274-f955-42b2-8581-9180712a3c78_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_088c8274-f955-42b2-8581-9180712a3c78" xlink:to="loc_srt_OwnershipDomain_088c8274-f955-42b2-8581-9180712a3c78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_7746d45c-a9ef-41d9-8a28-4f2a3f1af2ff" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_088c8274-f955-42b2-8581-9180712a3c78" xlink:to="loc_srt_OwnershipDomain_7746d45c-a9ef-41d9-8a28-4f2a3f1af2ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_ViantTechnologyLLCMember_341c9d63-8779-4c87-af2e-87cda436c4a0" xlink:href="dsp-20240930.xsd#dsp_ViantTechnologyLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_7746d45c-a9ef-41d9-8a28-4f2a3f1af2ff" xlink:to="loc_dsp_ViantTechnologyLLCMember_341c9d63-8779-4c87-af2e-87cda436c4a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_NumberOfUnitsOwned_0656fa48-a91a-4ab4-9c5b-03a6c313c647" xlink:href="dsp-20240930.xsd#dsp_NumberOfUnitsOwned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_1037d8e8-9b48-44f5-8b96-4b77b6c0ade8" xlink:to="loc_dsp_NumberOfUnitsOwned_0656fa48-a91a-4ab4-9c5b-03a6c313c647" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_0b7bb4f2-7611-4d63-9a4d-70f35310b7e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_1037d8e8-9b48-44f5-8b96-4b77b6c0ade8" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_0b7bb4f2-7611-4d63-9a4d-70f35310b7e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_EconomicInterestsOwnershipPercentage_949ae9df-a052-4dd9-b4e1-7af9e260cab6" xlink:href="dsp-20240930.xsd#dsp_EconomicInterestsOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_1037d8e8-9b48-44f5-8b96-4b77b6c0ade8" xlink:to="loc_dsp_EconomicInterestsOwnershipPercentage_949ae9df-a052-4dd9-b4e1-7af9e260cab6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_OwnershipInterestPercentage_3d16d9ce-b840-43c3-a614-16f9b9260257" xlink:href="dsp-20240930.xsd#dsp_OwnershipInterestPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_1037d8e8-9b48-44f5-8b96-4b77b6c0ade8" xlink:to="loc_dsp_OwnershipInterestPercentage_3d16d9ce-b840-43c3-a614-16f9b9260257" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.viantinc.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="dsp-20240930.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.viantinc.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_b8d33f31-2d78-4c17-8344-7554add77f5a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_7888a2e3-e360-427f-8956-d63b10aa9145" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_b8d33f31-2d78-4c17-8344-7554add77f5a" xlink:to="loc_us-gaap_SubsequentEventTable_7888a2e3-e360-427f-8956-d63b10aa9145" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_8a15b5d9-c80b-4fac-8f3b-4f4b97dbbebd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_7888a2e3-e360-427f-8956-d63b10aa9145" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_8a15b5d9-c80b-4fac-8f3b-4f4b97dbbebd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_8a15b5d9-c80b-4fac-8f3b-4f4b97dbbebd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8a15b5d9-c80b-4fac-8f3b-4f4b97dbbebd" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_8a15b5d9-c80b-4fac-8f3b-4f4b97dbbebd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_8e438426-f212-46c1-9024-611761a42f67" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8a15b5d9-c80b-4fac-8f3b-4f4b97dbbebd" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_8e438426-f212-46c1-9024-611761a42f67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_6c3e7714-3b18-463b-81a5-bd9d1c66ec1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_8e438426-f212-46c1-9024-611761a42f67" xlink:to="loc_us-gaap_SubsequentEventMember_6c3e7714-3b18-463b-81a5-bd9d1c66ec1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_8a61eae1-e289-43c6-8e30-781e4cf1940f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_7888a2e3-e360-427f-8956-d63b10aa9145" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_8a61eae1-e289-43c6-8e30-781e4cf1940f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8a61eae1-e289-43c6-8e30-781e4cf1940f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8a61eae1-e289-43c6-8e30-781e4cf1940f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8a61eae1-e289-43c6-8e30-781e4cf1940f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4f204825-374e-44e5-8a79-31946f06520c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8a61eae1-e289-43c6-8e30-781e4cf1940f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4f204825-374e-44e5-8a79-31946f06520c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_IRIS.TVInc.Member_dbe1ec28-9a32-4712-85c4-1c4a9e849127" xlink:href="dsp-20240930.xsd#dsp_IRIS.TVInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4f204825-374e-44e5-8a79-31946f06520c" xlink:to="loc_dsp_IRIS.TVInc.Member_dbe1ec28-9a32-4712-85c4-1c4a9e849127" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_b3147f5c-12f7-47e2-9e26-16f5fd1b9789" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_b8d33f31-2d78-4c17-8344-7554add77f5a" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_b3147f5c-12f7-47e2-9e26-16f5fd1b9789" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#AwardTypeOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_NonqualifiedStockOptionsMember_a1224c3c-8598-4bc2-91fa-c90da19e320e" xlink:href="dsp-20240930.xsd#dsp_NonqualifiedStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_dsp_NonqualifiedStockOptionsMember_a1224c3c-8598-4bc2-91fa-c90da19e320e" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_dsp_LarryMaddenMember_83c18836-a37f-40da-bc8e-bae8f6d77117" xlink:href="dsp-20240930.xsd#dsp_LarryMaddenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_dsp_LarryMaddenMember_83c18836-a37f-40da-bc8e-bae8f6d77117" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
