In addition to his stage career, Harrison also appeared in numerous films. His first starring role was opposite Vivien Leigh in the romantic comedy Storm in a Teacup (1937). Receiving critical acclaim for his performance in Major Barbara (1941), which was shot in London during the Blitz, his roles since then include Blithe Spirit (1945), Anna and the King of Siam (1946), The Ghost and Mrs. Muir (1947), Cleopatra (1963), My Fair Lady (1964, reprising his role as Henry Higgins which earned him the Academy Award for Best Actor), and the title role of the English doctor who talks to animals, Doctor Dolittle (1967).
In June 1989, Harrison was knighted by Queen Elizabeth II. In 1975, Harrison released his first autobiography. His second, A Damned Serious Business: My Life in Comedy, was published posthumously in 1991. Harrison was married six times and had two sons: Noel and Carey Harrison. He continued working in stage productions until shortly before his death from pancreatic cancer in June 1990 at the age of 82.