In addition to appearing as Rev. Mosby with actress Hayley Mills in "The Parent Trap" (1961), Carroll is remembered for his role as the frustrated banker haunted by the ghosts of George and Marion Kerby in the television series "Topper" (1953–1956), with co-stars Anne Jeffreys, Robert Sterling and Lee Patrick. He appeared as the older Father Fitzgibbon from 1962 to 1963 in ABC's "Going My Way", a series about two Roman Catholic priests at St. Dominic's parish in New York City. In 1963-1964, he portrayed John Miller in "Channing" on ABC. Carroll subsequently starred as spymaster Alexander Waverly on "The Man from U.N.C.L.E." (1964–1968). Several "U.N.C.L.E." films were derived from the series, and a spin-off television series, "The Girl from U.N.C.L.E." in 1966. He was one of the first actors to appear in two different television series as the same character. Leo G. Carroll is mentioned in "The Rocky Horror Picture Show" opening song "Science Fiction/Double Feature".