Leo G. Carroll was born October 25, 1892 to William and Catherine Carroll in Weedon Bec, Northamptonshire.
Leo G. Carroll made his debut on Broadway in 1912 in Rutherford & Son. In 1913, he appeared on Broadway in Everyman.
His acting career was on hold during World War I, when he served in the British Army.
After World War I, he returned to Broadway appearing in such plays as Havoc, The Constant Nymph, Speak Easy, The Perfect Alibi and The Green Bay Tree.
In 1934, he moved to Hollywood and made his film debut in Sadie McKee.
Leo G. Carroll is best known for his roles in six Alfred Hitchock films: Rebecca (1940), Suspicion (1941), Spellbound (1945), The Paradine Case (1947), Strangers on a Train (1951) and North By Northwest (1959). He appeared in more Hitchcock films than any other actor.
Leo G. Carroll also appeared in films such as The Casino Murder Case (1935), Wuthering Heights (1939), A Christmas Carol (1938), The Private Lives of Elizabeth Essex (1939), Waterloo Bridge (1940), Father of the Bride (1950), The Bad and The Beautiful (1952), The Swan (1956), and The Parent Trap (1961).
Leo G. Carroll's final film appearance was in One Spy Too Many (1966).
During Leo G. Carroll's film career he also frequently returned to his first love, Broadway. He appeared in 35 Broadway productions including Anne of England, The Late George Apley, You Never Can Tell, Mary Rose and Someone is Waiting.
On televison, Leo G. Carroll was Alexander Waverly on The Girl from U.N.C.L.E. and The Man from U.N.C.L.E. He would earn two Emmy nominations for Best Supporting Actor.
On October 16, 1972, Leo G. Carroll died iof pneumonia brought on by cancer, he was 79.