<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2016-09-12</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001583513</issuerCik>
        <issuerName>STG Group, Inc.</issuerName>
        <issuerTradingSymbol>STGG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001176532</rptOwnerCik>
            <rptOwnerName>LACOMBE PHILLIP E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O STG GROUP, INC.,</rptOwnerStreet1>
            <rptOwnerStreet2>11091 SUNSETHILLS ROAD, SUITE 200</rptOwnerStreet2>
            <rptOwnerCity>RESTON</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>20190</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and COO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <ownerSignature>
        <signatureName>/s/ Philip E. Lacombe</signatureName>
        <signatureDate>2016-09-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
