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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:18fd7ed0-bfb4-49dc-8075-a5ad19969680,g:421be0e6-194d-4b97-bc37-552d2d49a1ae-->
<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.blaize.com/role/Cover" xlink:type="simple" xlink:href="blz-20260324.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.blaize.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_d737647e-1478-42fa-b2c8-8c3a77352fa7" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_DocumentInformationTable_d737647e-1478-42fa-b2c8-8c3a77352fa7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_db6dae4e-7dda-4a5b-a61a-a3082388fbbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_d737647e-1478-42fa-b2c8-8c3a77352fa7" xlink:to="loc_us-gaap_StatementClassOfStockAxis_db6dae4e-7dda-4a5b-a61a-a3082388fbbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_db6dae4e-7dda-4a5b-a61a-a3082388fbbd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_db6dae4e-7dda-4a5b-a61a-a3082388fbbd" xlink:to="loc_us-gaap_ClassOfStockDomain_db6dae4e-7dda-4a5b-a61a-a3082388fbbd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5f6a5237-f3a9-4f4a-88ca-139a3d738eef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_db6dae4e-7dda-4a5b-a61a-a3082388fbbd" xlink:to="loc_us-gaap_ClassOfStockDomain_5f6a5237-f3a9-4f4a-88ca-139a3d738eef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_f4b97a22-4a43-479d-8545-b3b976c25648" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5f6a5237-f3a9-4f4a-88ca-139a3d738eef" xlink:to="loc_us-gaap_CommonStockMember_f4b97a22-4a43-479d-8545-b3b976c25648" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_8ac598dc-87d7-4061-9643-b5aa181a34d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5f6a5237-f3a9-4f4a-88ca-139a3d738eef" xlink:to="loc_us-gaap_WarrantMember_8ac598dc-87d7-4061-9643-b5aa181a34d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_5284f4c4-e44b-495f-986c-75a80e2d8a57" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_DocumentType_5284f4c4-e44b-495f-986c-75a80e2d8a57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_a07b2c54-5bc5-4037-93f0-2f947a269cd8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_DocumentPeriodEndDate_a07b2c54-5bc5-4037-93f0-2f947a269cd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_b3b94d73-f152-42e6-809b-5a60ce0d96e1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityRegistrantName_b3b94d73-f152-42e6-809b-5a60ce0d96e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_aa340626-44e6-4200-8987-c0777d73d8ba" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityIncorporationStateCountryCode_aa340626-44e6-4200-8987-c0777d73d8ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_45629e49-90a5-4864-a5db-1c784910cab4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityFileNumber_45629e49-90a5-4864-a5db-1c784910cab4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_e8153fcf-fd54-4aa5-8fb7-10901e736dd2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityTaxIdentificationNumber_e8153fcf-fd54-4aa5-8fb7-10901e736dd2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_9f4b1740-cb59-4139-b401-76f373d10537" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityAddressAddressLine1_9f4b1740-cb59-4139-b401-76f373d10537" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_16345f6a-4a84-48b2-8050-2e946b9c2338" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityAddressAddressLine2_16345f6a-4a84-48b2-8050-2e946b9c2338" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_a9b218fd-532d-4544-8243-3879814a0ca1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityAddressCityOrTown_a9b218fd-532d-4544-8243-3879814a0ca1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_cbfb20b8-3a31-4b09-b7bd-4dc9881b66b9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityAddressStateOrProvince_cbfb20b8-3a31-4b09-b7bd-4dc9881b66b9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_b3a68662-c04c-466c-8f39-406724f94619" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityAddressPostalZipCode_b3a68662-c04c-466c-8f39-406724f94619" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_09975e75-3acf-4cc8-be72-f6ef69b06060" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_CityAreaCode_09975e75-3acf-4cc8-be72-f6ef69b06060" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_74ab9808-9d9e-4e47-96e0-14209979b99c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_LocalPhoneNumber_74ab9808-9d9e-4e47-96e0-14209979b99c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_2acedd79-b451-40d3-a35c-0337252fe676" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_WrittenCommunications_2acedd79-b451-40d3-a35c-0337252fe676" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_29c52cc4-d637-4a48-8bdd-4d7cb552610b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_SolicitingMaterial_29c52cc4-d637-4a48-8bdd-4d7cb552610b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_64672ebf-c568-4556-a577-c90c06f3bce2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_PreCommencementTenderOffer_64672ebf-c568-4556-a577-c90c06f3bce2" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_052c18b7-a9db-4501-9b9f-2706196a4513" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_052c18b7-a9db-4501-9b9f-2706196a4513" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_69c74568-f2cf-4a87-af58-a59cacb588fe" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_Security12bTitle_69c74568-f2cf-4a87-af58-a59cacb588fe" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_13e791f5-2bf2-44da-a092-709643cfd2de" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_TradingSymbol_13e791f5-2bf2-44da-a092-709643cfd2de" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_ffaeb08a-f4fc-4e65-ae65-d465774c5370" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_SecurityExchangeName_ffaeb08a-f4fc-4e65-ae65-d465774c5370" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_1ea5bac5-016b-408d-a1a5-2701781fdce5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityEmergingGrowthCompany_1ea5bac5-016b-408d-a1a5-2701781fdce5" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_e709d083-3ef9-412d-ab86-35d69d4af830" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityExTransitionPeriod_e709d083-3ef9-412d-ab86-35d69d4af830" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_ee7cdcb6-b509-45f8-8215-46df09a321b9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_EntityCentralIndexKey_ee7cdcb6-b509-45f8-8215-46df09a321b9" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_1092e464-ae61-49f0-bc75-a75ecbcb0470" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_df97c673-77ba-4c56-b54e-9a1f48c4735f" xlink:to="loc_dei_AmendmentFlag_1092e464-ae61-49f0-bc75-a75ecbcb0470" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
