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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-11-16</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000783603</issuerCik>
        <issuerName>AMERICAN SAFETY INSURANCE HOLDINGS LTD</issuerName>
        <issuerTradingSymbol>ASI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001486659</rptOwnerCik>
            <rptOwnerName>Cloutier Guy</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>44 CHURCH STREET</rptOwnerStreet1>
            <rptOwnerStreet2>P.O. BOX HM2064</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM 11</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Actuary</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-11-16</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2010-11-16</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5621</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.10</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>57850</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (Right To Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>19.55</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2012-03-17</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-03-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                    <footnoteId id="F2"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (Right To Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>17.95</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-03-01</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2018-03-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2500</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (Right To Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.10</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2010-03-09</value>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-03-09</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>11241</value>
                    <footnoteId id="F4"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18741</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (Right To Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>14.34</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2011-03-05</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-03-05</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10941</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29682</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Exercised portion of opition granted on 3/9/2009.</footnote>
        <footnote id="F2">Options awarded pursuant to the Company's 2007 Incentive Stock Option Plan. These options have a three-year vesting schedule, pursuant to which the shares underlying the options shall cliff vest on the 5th anniversary of the date of grant. The date shown is the date the first vested number of shares becomes/became exercisable.</footnote>
        <footnote id="F3">Options awarded pursuant to the Company's 2007 Incentive Stock Option Plan. These options have a three-year vesting schedule, pursuant to which the shares underlying the options shall vest in one-third increments commencing one year after the date of grant. The date shown is the date the first vested number of shares becomes/became exercisable.</footnote>
        <footnote id="F4">Options awarded pursuant to the Company's 2007 Incentive Stock Option Plan. These options have a three-year vesting schedule, pursuant to which the shares underlying the options shall vest in one-third increments commencing one year after the date of grant. The date shown is the date the first vested number of shares becomes/became exercisable. 5,621 options were exercised on 11/16/2010 of 16,862 originally issued.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Guy Cloutier</signatureName>
        <signatureDate>2010-11-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
