J. Keirn Brennan (November 24, 1873 – February 4, 1948) was an American songwriter. He joined ASCAP as a charter member in 1914 and collaborated with many notable songwriters. He is probably best known for co-writing the 1929 film The Show of Shows.
Born in San Francisco, California, his musical collaborators included Harry Akst, Ernest Ball, Walter Donaldson, Rudolf Friml, Karl Hajos, Billy Hill, Werner Janssen, Chauncey Olcott, and Maurice Rubens. His song compositions include Sure a Little Bit of Heaven (1914), Dear Little Boy of Mine, Goodbye, Good Luck, God Bless You, Empty Saddles, Turn Back the Universe, When My Boy Comes Home, A Little Bit of Love, My Bird of Paradise, I'll Follow the Trail, You Hold My Heart, Let the Rest of the World Go By and Ireland Is Ireland to Me.
He died in Hollywood, California.