Flaherty served in the U.S. Army during the Pancho Villa Expedition and then as an U.S. Army Air Service pilot in World War I. Flaherty was a popular Washington, D.C., athlete and coach, who went on to become a professional baseball and football player and was in the bullpen for John McGraw's New York Giants during the 1921 World Series, and punted for George Halas' Chicago Bears.

[2] After his professional athletic career ended, he went into the music publishing business with the legendary DeSylva, Brown and Henderson during the time of Mayor Jimmy Walker in New York.

Flaherty relocated to Hollywood to take a position as a producer at 20th Century Fox for the owner Joseph P. Kennedy when the Great Depression began.

Flaherty can be seen in roles both large and small in films such as Death on the Diamond (1934), Mutiny on the Bounty (1935), Sergeant York (1941), Yankee Doodle Dandy (1942), The Pride of the Yankees (1942), It Happened in Flatbush (1942), and a bit appearance as a bewildered Marine in Stage Door Canteen.

Outside the realm of baseball, Flaherty was usually cast in blunt, muscle-bound roles, notably Fredric March's taciturn male nurse "Cuddles" in A Star is Born (1937).