<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-05-06</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000946090</issuerCik>
        <issuerName>FIRST MARINER BANCORP</issuerName>
        <issuerTradingSymbol>FMAR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001029384</rptOwnerCik>
            <rptOwnerName>STOLER LEONARD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeSecurity>
        <securityTitle>
            <value>STOCK OPTION (RIGHT TO BUY)</value>
        </securityTitle>
        <conversionOrExercisePrice>
            <value>13.52</value>
        </conversionOrExercisePrice>
        <transactionDate>
            <value>2003-05-06</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>A</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>500</value>
            </transactionShares>
            <transactionValue>
                <value>13.52</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <exerciseDate>
            <value>2003-05-06</value>
            <footnoteId id="F1"/>
        </exerciseDate>
        <expirationDate>
            <value>2013-05-06</value>
        </expirationDate>
        <underlyingSecurity>
            <underlyingSecurityTitle>
                <value>COMMON STOCK</value>
            </underlyingSecurityTitle>
            <underlyingSecurityShares>
                <value>500</value>
            </underlyingSecurityShares>
        </underlyingSecurity>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>500</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </derivativeSecurity>

    <footnotes>
        <footnote id="F1">ONE THIRD OF THE OPTIONS ARE EXERCISABLE ON THE GRANT DATE, ONE THIRD OF THE OPTIONS ARE EXERCISABLE ON THE FIRST ANNIVERSARY OF THE GRANT DATE AND ONE THIRD OF THE OPTIONS ARE EXERCISABLE ON THE SECOND ANNIVERSARY OF THE GRANT DATE.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ LEONARD STOLER</signatureName>
        <signatureDate>2003-05-06</signatureDate>
    </ownerSignature>

</ownershipDocument>

