John's early career in commercial art took an unexpected turn when he filled in for a sick friend in an amateur production, catching the eye of renowned actress Sybil Thorndike, who recognized his untapped potential. This led to a stint in repertory work at Watford and Crewe, before he was invited to join London's esteemed Old Vic in 1936 by Tyrone Guthrie. During his time at the Old Vic, John appeared in notable productions such as 'Love's Labours Lost' and 'Twelfth Night', showcasing his versatility as an actor.
In 1937, John made his mark in the film industry with his debut in 'The Conquest of the Air' and a BBC television production of 'The Harmfulness of Tobacco'. However, his acting career was put on hold when World War II broke out, and John was attached to the British Embassy in Stockholm, where he worked in coding and decoding.
After the war, John found himself in California, on the cusp of returning to England when he was offered a role in 'The Shanghai Gesture' (1941),marking the beginning of a long and illustrious film career. He went on to star in numerous iconic films, including 'Mrs. Miniver' (1942),'Jane Eyre' (1943),'Madame Bovary' (1949),'Gigi' (1958),and 'Gambit' (1966).
John also made a significant impact on the stage, making his Broadway debut in 'He Who Gets Slapped' (1946) and going on to appear in numerous productions, including 'Montsarrat' (1948) and 'The Waltz of the Toreadors' (1957). His prolific television career saw him appear in episodes of 'Alfred Hitchcock Presents' (1955),'The Man from U.N.C.L.E.' (1964),and 'Bewitched' (1964),showcasing his impressive range as an actor.