Exhibit 5.1

22 March, 2013

Matter No.: 342069

Doc Ref: 2783925

(441) 299 4982

mary.ward@conyersdill.com

Tower Group International, Ltd.

Crown House

4 Par-La-Ville Road

Hamilton HM08

Bermuda

Dear Sirs,

Tower Group International, Ltd. (the “Company”)

We have acted as special Bermuda legal counsel to the Company, the successor issuer to Tower Group, Inc. pursuant to the Agreement and Plan of Merger dated 30 July 2012 that became effective on March 13 2013, in connection with Post-Effective Amendment No. 1 to the Registration Statements on Form S-8 (Registration Number 333-120320 and Registration Number 333-151801) to be filed with the Securities and Exchange Commission (the “Commission”) on 22 March, 2013 (the “Post-Effective Amendment”, which term does not include any other document or agreement whether or not specifically referred to therein or attached as an exhibit or schedule thereto) relating to an aggregate of up to 2,944,090 common shares, par value US$0.01 per share (the “Common Shares”), issuable pursuant to the Tower Group, Inc. 2004 Long Term Equity Compensation Plan (the “Plan”, which term does not include any other document or agreement whether or not specifically referred to therein or attached as an exhibit or schedule thereto) pursuant to Rule 414 under the United States Securities Act of 1933, as amended (the “Securities Act”), to reflect that the Company succeeded to the Registration Statement.

For the purposes of giving this opinion, we have examined copies of the Registration Statements and the Plan. We have also reviewed the memorandum of association and the bye-laws of the Company, each certified by the Assistant Secretary of the Company on 21 March, 2013 and minutes of a meeting of its directors held on 15 March, 2013 certified by the Secretary of the Company on 22 March, 2013 (the “Resolutions”) and such other documents and made such enquires as to questions of law as we have deemed necessary in order to render the opinion set forth below.

We have assumed (a) the genuineness and authenticity of all signatures and the conformity to the originals of all copies (whether or not certified) of all documents examined by us and the authenticity and completeness of the originals from which such copies were taken, (b) that where a document has been examined by us in draft form, it will be or has been executed and/or filed in the form of that draft, and where a number of drafts of a document have been examined by us all changes thereto have been marked or otherwise drawn to our attention, (c) the accuracy and completeness of all factual representations made in the Post-Effective Amendment, the Plan and other documents reviewed by us, (d) that the Resolutions were passed at one or more duly convened, constituted and quorate meetings, or by unanimous written resolutions, remain in full force and effect and have not been rescinded or amended, (e) that there is no provision of the law of any jurisdiction, other than Bermuda, which would have any implication in relation to the opinions expressed herein, (f) the validity and binding effect under the laws of the state of New York of the Plan in accordance with its terms; (g) that there is no provision of any award agreement or option which would have any implication in relation to the opinions expressed herein; (h) that, upon the issue of any Common Shares, the Company will receive consideration for the full issue price thereof which shall be equal to at least the par value thereof, (i) that on the date of issuance of any of the Common Shares the Company will have sufficient authorised but unissued common shares, (j) that on the date of issuance of any award or option under a Plan, the Company will be able to pay its liabilities as they become due, (k) that the Company’s shares will be listed on an appointed stock exchange, as defined in the Companies Act 1981, as amended, and the consent to the issue and free transfer of the Common Shares given by the Bermuda Monetary Authority dated June 1 2005 will not have been revoked or amended at the time of issuance of any Common Shares.

We express no opinion with respect to the issuance of shares pursuant to any provision of the Plan that purports to obligate the Company to issue shares following the commencement of a winding up or liquidation. We have made no investigation of and express no opinion in relation to the laws of any jurisdiction other than Bermuda. This opinion is to be governed by and construed in accordance with the laws of Bermuda and is limited to and is given on the basis of the current law and practice in Bermuda. This opinion is issued solely for the purposes of the filing of the Registration Statement and the issuance of the Common Shares by the Company pursuant to the Plan and is not to be relied upon in respect of any other matter.

On the basis of, and subject to, the foregoing, we are of the opinion that:

1. The Company is duly incorporated and existing under the laws of Bermuda in good standing (meaning solely that it has not failed to make any filing with any Bermuda government authority or to pay any Bermuda government fees or tax which would make it liable to be struck off the Register of Companies and thereby cease to exist under the laws of Bermuda).

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2. When issued and paid for in accordance with the terms of the Plan, the Common Shares will be validly issued, fully paid and non-assessable (which term means when used herein that no further sums are required to be paid by the holders thereof in connection with the issue of such shares).

We consent to the filing of this opinion as an exhibit to the Registration Statement. In giving such consent, we do not hereby admit that we are experts within the meaning of Section 11 of the Securities Act or that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the Rules and Regulations of the Commission promulgated thereunder.

Yours faithfully,

Conyers Dill & Pearman Limited

/s/ Conyers Dill & Pearman Limited

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