Born in Wexford in May 1919 to John O’Herlihy and Ellen née Hanton, he was educated in CBS, Dún Laoghaire and University College Dublin obtaining his degree in architecture in 1945. He married Elsie Bennett in University Church, St Stephen’s Green, Dublin on 16 August 1945.

His first major Irish break occurred in 1944, playing the lead role in the world premiere of Seán O’Casey’s play Red Roses for Me. A part in Carol Reed’s Odd Man Out in 1947 effectively opened the door to Hollywood and a long and prolific career in film and television. Credited with over seventy motion pictures, over two hundred and fifty television productions and over fifty stage plays. Established the Hollywood School of Drama in 1955. Joined Orson Welles’ Mercury Theatre in 1948. Starred, alongside Welles, in the stage and film version of Shakespeare’s Macbeth in which he played the character Macduff. Offered lead part in Luis Buñuel’s The Adventures of Robinson Crusoe in 1953–54. Nominated for an academy award in the category of best actor for his performance as Crusoe. Subsequently focused on character parts which included Marshall Ney in Waterloo (1970–71), Franklin D. Roosevelt in MacArthur (1977–78), the sinister Old Man in Robocop I and Robocop II (1987, 1990), Mark Twain in the television drama Mark Twain: Beneath the Laughter (1979) and Joe Kennedy in the television film The Rat Pack (1998). He also appeared as the character Mr Brown in John Huston’s final film The Dead (1987). In America O’Herlihy was well known for his television work in many popular series. He died in his home in Malibu, Claifornia on 17th February 2005.