More parts followed, often playing doctors or butlers, but with some variations from that norm. He made notable appearances as Marley's ghost in A Christmas Carol (1938) and as Joseph in Wuthering Heights (1939). In Father of the Bride he played a unctious wedding caterer. In the 1951 film The Desert Fox: The Story of Rommel, he played a sympathetic Gerd von Rundstedt, not mentioning any of the war crimes Rundstedt was later charged with, instead presenting him as a tragic, resigned figure completely disillusioned with Hitler.
In the twenties, Carroll played the lead in a successful Broadway play, The Green Bay Tree, and in 1941 starred with Vincent Price and Judith Evelyn in the smash hit Angel Street, which ran for three years at the Golden Theatre on 45th Street. After that closed, he starred in the title role in J.P. Marquand's The Late George Apley.
Carroll is perhaps most well-known for his roles in six of Alfred Hitchcock's films. As with earlier roles he was often cast as doctors or other figure of authority, such as the spymaster The Professor in North by Northwest. He is also remembered for his role as the frustrated banker haunted by the ghosts of George and Marion Kirby, in the 1950s television series Topper (1953–56) which also starred Anne Jeffreys, Robert Sterling and Lee Patrick; and later as spymaster Alexander Waverly on The Man from U.N.C.L.E. (1964–68), echoing his earlier work for Hitchcock. Several U.N.C.L.E. films followed, and a spin-off The Girl from U.N.C.L.E. (1966). He was one of the first actors to appear in two different television series as the same character.
Is mentioned in the song Magdalena from the 1972 Frank Zappa and the Mothers album Just Another Band from LA.
" the stars that say Jon Provost and Leo G. Carroll together"Is mentioned in the song "Science Fiction Double Feature," in the "Rocky Horror Picture Show," with the lines "I knew Leo G. Carroll, was over a barrel, when Tarantula took to the hills."