-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 NHt32rX33vopp6+UqVB3Ob3HspkVI5z9tom8wvb2dKdFVnOI7f8EJiNDjYdiyOpZ
 5zniSN5ydPv931FPGx7+iw==

<SEC-DOCUMENT>0001140361-06-015615.txt : 20061107
<SEC-HEADER>0001140361-06-015615.hdr.sgml : 20061107
<ACCEPTANCE-DATETIME>20061107154014
ACCESSION NUMBER:		0001140361-06-015615
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20061108
FILED AS OF DATE:		20061107
DATE AS OF CHANGE:		20061107

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			OneBeacon Insurance Group, Ltd.
		CENTRAL INDEX KEY:			0001369817
		STANDARD INDUSTRIAL CLASSIFICATION:	FIRE, MARINE & CASUALTY INSURANCE [6331]
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			D0
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		80 SOUTH MAIN STREET
		CITY:			HANOVER
		STATE:			NH
		ZIP:			03755
		BUSINESS PHONE:		6036402206

	MAIL ADDRESS:	
		STREET 1:		80 SOUTH MAIN STREET
		CITY:			HANOVER
		STATE:			NH
		ZIP:			03755

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	OneBeacon Holdings (Bermuda) Ltd.
		DATE OF NAME CHANGE:	20060721

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FORSYTH THOMAS LESTER
		CENTRAL INDEX KEY:			0001378158

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-33128
		FILM NUMBER:		061193835

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		603-640-2206

	MAIL ADDRESS:	
		STREET 1:		C/O WHITE MOUNTAINS INSURANCE GROUP
		STREET 2:		80 SOUTH MAIN STREET
		CITY:			HANOVER
		STATE:			NH
		ZIP:			03755
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2006-11-08</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001369817</issuerCik>
        <issuerName>OneBeacon Insurance Group, Ltd.</issuerName>
        <issuerTradingSymbol>OB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001378158</rptOwnerCik>
            <rptOwnerName>FORSYTH THOMAS LESTER</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ONEBEACON INSURANCE GROUP, LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BEACON STREET</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02108</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Secretary</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class A Common Shares</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Option to buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>30</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2007-10-18</value>
            </exerciseDate>
            <expirationDate>
                <value>2013-04-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>16464</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Option to buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>30.00</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2008-10-18</value>
            </exerciseDate>
            <expirationDate>
                <value>2014-04-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>16464</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Option to buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>30.00</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-10-18</value>
            </exerciseDate>
            <expirationDate>
                <value>2015-04-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>16463</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Thomas L. Forsyth</signatureName>
        <signatureDate>2006-11-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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