Exhibit 5.1

First Commonwealth

Financial Corporation

Executive Offices

Old Courthouse Square

22 North Sixth Street

Indiana, Pennsylvania 15701-0400

724.349.7220 Phone

724.464.1112 Fax

www.fcbanking.com

May 8, 2009

First Commonwealth Financial Corporation

22 North 6th Street

Indiana, PA 15701

Re: Registration Statement on Form S-3 for the issuance of Shares of Common Stock Pursuant to the First Commonwealth Financial Corporation Direct Stock Purchase and Dividend Reinvestment Plan (“Registration Statement”)

Ladies and Gentlemen:

I have acted as counsel to First Commonwealth Financial Corporation, a Pennsylvania corporation (“Company”), in connection with the proposed issuance of up to 5,000,000 shares of the Company’s common stock, par value $1.00 per share (“Common Stock”), pursuant to the First Commonwealth Financial Corporation Direct Stock Purchase and Dividend Reinvestment Plan.

As counsel for the Company I have made such legal and factual examinations and inquiries as I deem advisable for the purpose of rendering this opinion. In addition, I have examined such documents and materials, including the Articles of Incorporation, By-Laws, and other corporate records of the Company, as I have deemed necessary for the purpose of this opinion.

On the basis of the foregoing, in my opinion, the 5,000,000 shares of Common Stock registered for issuance pursuant to the Registration Statement, have been duly authorized and, when issued as contemplated by the Registration Statement, will be validly issued, fully paid and non-assessable shares of Common Stock of the Company.

I hereby consent to the use of my name in the Registration Statement under the heading “Legal Opinion” and to the filing of this opinion as part of the Registration Statement and amendments thereto.

Very Truly Yours,

/s/ Matthew C. Tomb

Matthew C. Tomb