Francis John Joseph Brennan (May 7, 1894 – July 2, 1968) was an American cardinal of the Catholic Church.

Upon his return to the United States, Brennan did pastoral work in the Archdiocese of Philadelphia from 1924 to 1928, when he became a member of the faculty at his alma mater, St. Charles Seminary.

Described as a "brilliant canon lawyer",[1] he was named an auditor of the Roman Rota on August 1, 1940, rising to become its dean on December 14, 1959.

On June 10, 1967, Brennan was appointed Titular Archbishop of Tubunae in Mauretania by Pope Paul VI.

He received his episcopal consecration on the following June 25 from Cardinal Eugène-Gabriel-Gervais-Laurent Tisserant, with Bishops Joseph Carroll McCormick and Luigi Faveri serving as co-consecrators, at the church of Sant'Anselmo all'Aventino.