Exhibit 5.1

September 26, 2013

UIL Holdings Corporation
157 Church Street
New Haven, CT 06506

Ladies and Gentlemen:

We have acted as counsel to UIL Holdings Corporation, a Connecticut corporation (the “Company”), in connection with the issuance of up to 5,750,000 shares of common stock of the Company, no par value (including shares that may be issued upon exercise of an option granted to the underwriters to purchase up to 750,000 shares of common stock to cover over-allotments) (collectively, the “Shares”), pursuant to an Underwriting Agreement, dated as of September 26, 2013 (the “Underwriting Agreement”) among the Company, J.P. Morgan Securities LLC, Merrill Lynch, Pierce, Fenner & Smith Incorporated and Wells Fargo Securities, LLC, as representatives of the several underwriters listed in Schedule 1 to the Underwriting Agreement. The Shares will be issued in an underwritten public offering pursuant to the Company’s Registration Statement on Form S-3 (Registration No. 333-179998), as filed with the Securities and Exchange Commission on March 8, 2012 (at the time it became effective, the “Registration Statement”), pursuant to the Securities Act of 1933, as amended (the “Securities Act”), and the related prospectus dated March 8, 2012 and prospectus supplement dated September 26, 2013 (collectively, the “Prospectus”).

We have examined the Registration Statement, the Prospectus and documents and records of the Company and other documents, matters of fact and questions of law that we have deemed necessary for the purposes of this opinion. In our examination, we have assumed the authenticity of original documents and the

UIL Holdings Corporation

September 26, 2013

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genuineness of all signatures, the conformity to the originals of all documents submitted to us as copies, and the truth, accuracy, and completeness of the information, representations, and warranties contained in the records, documents, instruments, and certificates we have reviewed.

Based upon the foregoing, we are of the opinion that the Shares have been duly authorized and, when issued in accordance with the terms of the Underwriting Agreement, the Registration Statement and the Prospectus, the Shares will be validly issued, fully paid and nonassessable.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Current Report on Form 8-K of even date herewith, incorporated by reference into the Registration Statement, and to the reference to this firm under the heading “Legal matters” in the Prospectus. In giving this consent, we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or related rules, nor do we admit that we are experts with respect to any part of the Registration Statement within the meaning of the term “expert” as used in the Securities Act or related rules.

Very truly yours,