Exhibit 5.1

[Letterhead of Hogan Lovells US LLP]

October 28, 2011

Board of Directors

CapitalSource Inc.

5404 Wisconsin Avenue, 2nd Floor

Chevy Chase, MD 20815

Re: Resale Registration of Common Stock on behalf of Selling Stockholders

Ladies and Gentlemen:

We are acting as counsel to CapitalSource Inc., a Delaware corporation (the “Company”), in connection with the resale registration of 11,608,587 shares (the “Shares”) of its common stock, par value $0.01 per share (“Common Stock”), which Shares may be sold by certain selling stockholders from time to time, as described in the prospectus supplement dated October 28, 2011 (the “Prospectus Supplement”) and the accompanying prospectus dated October 27, 2011 (the “Base Prospectus” and, together with the Prospectus Supplement, the “Prospectus”) that form part of the Company’s effective registration statement on Form S-3 (Reg. No. 333-177562) (the “Registration Statement”). This opinion letter is furnished to you at your request to enable you to fulfill the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. §229.601(b)(5), in connection with the Registration Statement.

For purposes of this opinion letter, we have examined copies of such agreements, instruments and documents as we have deemed an appropriate basis on which to render the opinions hereinafter expressed. In our examination of the aforesaid documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to us, the authenticity of all original documents, and the conformity to authentic original documents of all documents submitted to us as copies (including telecopies). As to all matters of fact, we have relied on the representations and statements of fact made in the documents so reviewed, and we have not independently established the facts so relied on. This opinion letter is given, and all statements herein are made, in the context of the foregoing.

This opinion letter is based as to matters of law solely on the Delaware General Corporation Law, as amended. We express no opinion herein as to any other laws, statutes, ordinances, rules, or regulations (and in particular, we express no opinion as to any effect that such other laws, statutes, ordinances, rules, or regulations may have on the opinions expressed herein).

Based upon, subject to and limited by the foregoing, we are of the opinion that the Shares are validly issued, fully paid and nonassessable.

This opinion letter has been prepared for use in connection with the filing by the Company of a Current Report on Form 8-K, which Form 8-K will be incorporated by reference in the Prospectus constituting part of the Registration Statement. We assume no obligation to advise you of any changes in the foregoing subsequent to the delivery of this opinion letter.

CapitalSource Inc.

October 28, 2011

Page 2

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the above-described Form 8-K and to the reference to this firm under the caption “Legal Matters” in the Prospectus constituting a part of the Registration Statement. In giving this consent, we do not thereby admit that we are an “expert” within the meaning of the Securities Act of 1933, as amended.