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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019dfac4-2b7a-7ba8-b730-5e7e156526ec,g:51e629e0-0aec-4ab6-bc48-834cbca132c3-->
<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-20260505.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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019dfac4-2b7a-7d80-9c25-1babcc9f5fe1" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_DocumentInformationTable_019dfac4-2b7a-7d80-9c25-1babcc9f5fe1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019dfac4-2b7a-77e2-9227-f1066bf62f3b" 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_019dfac4-2b7a-7d80-9c25-1babcc9f5fe1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019dfac4-2b7a-77e2-9227-f1066bf62f3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dfac4-2b7a-77e2-9227-f1066bf62f3b_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_019dfac4-2b7a-77e2-9227-f1066bf62f3b" xlink:to="loc_us-gaap_ClassOfStockDomain_019dfac4-2b7a-77e2-9227-f1066bf62f3b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019dfac4-2b7a-7dd7-953f-f834c675b346" 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_019dfac4-2b7a-77e2-9227-f1066bf62f3b" xlink:to="loc_us-gaap_ClassOfStockDomain_019dfac4-2b7a-7dd7-953f-f834c675b346" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019dfac4-2b7a-702c-96e2-9ba6df05ce72" 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_019dfac4-2b7a-7dd7-953f-f834c675b346" xlink:to="loc_us-gaap_CommonStockMember_019dfac4-2b7a-702c-96e2-9ba6df05ce72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019dfac4-2b7a-7002-bc9b-219c87f6262c" 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_019dfac4-2b7a-7dd7-953f-f834c675b346" xlink:to="loc_us-gaap_WarrantMember_019dfac4-2b7a-7002-bc9b-219c87f6262c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019dfac4-2b7a-78bd-ac3a-204630d9de58" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_DocumentType_019dfac4-2b7a-78bd-ac3a-204630d9de58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019dfac4-2b7a-7192-acde-b2400ab7cb85" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_DocumentPeriodEndDate_019dfac4-2b7a-7192-acde-b2400ab7cb85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019dfac4-2b7a-7c7d-8ce4-539afe3d464a" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityRegistrantName_019dfac4-2b7a-7c7d-8ce4-539afe3d464a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019dfac4-2b7a-765d-943c-bc406bd43c86" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019dfac4-2b7a-765d-943c-bc406bd43c86" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019dfac4-2b7a-758b-ad93-99efac0c1aef" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityFileNumber_019dfac4-2b7a-758b-ad93-99efac0c1aef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019dfac4-2b7a-7ab1-80b7-97e7a05f02e4" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityTaxIdentificationNumber_019dfac4-2b7a-7ab1-80b7-97e7a05f02e4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019dfac4-2b7a-758f-81d4-f1b8fddfb7de" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityAddressAddressLine1_019dfac4-2b7a-758f-81d4-f1b8fddfb7de" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019dfac4-2b7a-7787-861d-0699f206cf3d" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityAddressAddressLine2_019dfac4-2b7a-7787-861d-0699f206cf3d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019dfac4-2b7a-7c30-9bf1-5e29e4f0b98a" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityAddressCityOrTown_019dfac4-2b7a-7c30-9bf1-5e29e4f0b98a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019dfac4-2b7a-7ee3-8abe-ff230361554b" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityAddressStateOrProvince_019dfac4-2b7a-7ee3-8abe-ff230361554b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019dfac4-2b7a-78b7-8e01-ce1c1231f26c" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityAddressPostalZipCode_019dfac4-2b7a-78b7-8e01-ce1c1231f26c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019dfac4-2b7a-7add-abe3-ac702c45895e" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_CityAreaCode_019dfac4-2b7a-7add-abe3-ac702c45895e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019dfac4-2b7a-744e-a70f-97a781824f90" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_LocalPhoneNumber_019dfac4-2b7a-744e-a70f-97a781824f90" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019dfac4-2b7a-71dd-ac58-22004ba793f3" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_WrittenCommunications_019dfac4-2b7a-71dd-ac58-22004ba793f3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019dfac4-2b7a-7751-8323-34319968c055" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_SolicitingMaterial_019dfac4-2b7a-7751-8323-34319968c055" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019dfac4-2b7a-7902-a5d2-4bf4ea150b73" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_PreCommencementTenderOffer_019dfac4-2b7a-7902-a5d2-4bf4ea150b73" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019dfac4-2b7a-7049-86fd-3002268f072b" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019dfac4-2b7a-7049-86fd-3002268f072b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019dfac4-2b7a-7557-8278-65803f2cf1ac" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_Security12bTitle_019dfac4-2b7a-7557-8278-65803f2cf1ac" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019dfac4-2b7a-78fe-a722-f2a04ca2e3c7" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_TradingSymbol_019dfac4-2b7a-78fe-a722-f2a04ca2e3c7" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019dfac4-2b7a-7f45-8237-8ce8e968b470" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_SecurityExchangeName_019dfac4-2b7a-7f45-8237-8ce8e968b470" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019dfac4-2b7a-7c4d-a1fc-08ee287514df" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityEmergingGrowthCompany_019dfac4-2b7a-7c4d-a1fc-08ee287514df" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_019dfac4-2b7a-7b0e-82d6-38df9e3ecb81" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityExTransitionPeriod_019dfac4-2b7a-7b0e-82d6-38df9e3ecb81" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019dfac4-2b7a-7007-bbdd-b382d17dfcb3" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_EntityCentralIndexKey_019dfac4-2b7a-7007-bbdd-b382d17dfcb3" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019dfac4-2b7a-7cf7-bdd0-18147e28ff12" 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_019dfac4-2b7a-708c-b41e-346e8c8ce80d" xlink:to="loc_dei_AmendmentFlag_019dfac4-2b7a-7cf7-bdd0-18147e28ff12" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
