EXHIBIT 5.1

EXHIBIT 23.4

[LETTERHEAD OF SULLIVAN & CROMWELL LLP]

August 21 , 2006

First Community Bancorp,

6110 El Tordo, PO Box 2388,

Rancho Santa Fe, California 92067.

Ladies and Gentlemen:

In connection with the registration under the Securities Act of 1933 (the “Act”) of 4,612,820 shares (the “Securities”) of common stock, without par value, of First Community Bancorp, a California corporation (the “Company”), to be issued in connection with the Agreement and Plan of Merger, dated as of May 15, 2006, by and between the Company and Community Bancorp Inc., a Delaware corporation, we, as your counsel, have examined such corporate records, certificates and other documents, and such questions of law, as we have considered necessary or appropriate for the purposes of this opinion.

Upon the basis of such examination, we advise you that, in our opinion, when the registration statement relating to the Securities (the “Registration Statement”) has become effective under the Act, and the Securities have been duly issued as contemplated by the Registration Statement, the Securities will be validly issued, fully paid and nonassessable.

The foregoing opinion is limited to the federal laws of the United States and the Corporations Code of the State of California, and we are expressing no opinion with respect to the laws of any other jurisdiction.

We have relied as to certain factual matters on information obtained from public officials, officers of the Company and other sources believed by us to be responsible.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference to us under the heading “Validity of Common Stock” in the Prospectus. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act.

Very truly yours,

/s/    SULLIVAN & CROMWELL LLP