Biography in: "The Scribner Encyclopedia of American Lives". Volume One, 1981-1985, pages 607-608. New York: Charles Scribner's Sons, 1998.
Daughter Kathleen Brigid was born in June, 1946.
Films co-starring Pat O'Brien and James Cagney were these 9: Here Comes the Navy (1934), Ceiling Zero (1936), Torrid Zone (1940), Devil Dogs of the Air (1935), The Irish in Us (1935), Boy Meets Girl (1938), Angels with Dirty Faces (1938); The Fighting 69th (1940), as well as their finale together, four decades later, Ragtime (1981).
Had been playing Walter Burns in "The Front Page" on Broadway before being tapped to appear in the 1931 film (The Front Page (1931)). The studio, confusing Burns with the other lead role, Hildy Johnson, offered O'Brien the latter role, assuming it was the one he had played onstage. He took the job, not informing them of their mistake.
He and his wife had one biological child and 3 adopted children: Sean O'Brien, Terry O'Brien, Brigid O'Brien, and Mavourneen O'Brien.
He wore a toupee.
His final acting role was as a guest star in an episode of "Happy Days" (1974). The show was set in Milwaukee, WI, which was O'Brien's home town.
Pat was a great personal friend of fellow Irish-American actor James Cagney, from the early days of their career right up to Pat's death in 1983. They also starred in seven films together, Pat often playing the role of a Catholic priest.
Politically he was extremely right-wing, so much so that he was termed "a near-fascist", mainly because of his strong support of Generalissimo Francisco Franco during the Spanish Civil War.