A former advertising copywriter, he made his stage debut in a walk-on part in 1934. In 1941 he joined the Royal Navy as an Ordinary Seaman and obtained a commission the following vear. In 1942 he was given special leave to make his New York stage debut in a propaganda play, Flare Path.

After this, he resumed command of various coastal vessels and landing craft in the Mediterranean, ferrying supplies to Yugoslavian partisans. His landing, craft was also the First to hit the beach in the invasion of Sicily in July 1943 when he read the signal wrong and landed an hour early.

After the war, he gained wide popularity in a string of bright British comedies and managed to look astonishingly different from film to film (he played eight parts, including a woman, in the black comedy Kind Hearts and Coronets). He also excelled in dramatic portrayals and won the "best actor" Academy Award for his excellent character study in The Bridge on the River Kwai (1957).

Younger audiences know him better as the wise old spiritual warrior Obi-Wan Kenobi in the Star Wars trilogy. However, he hated the banality of the character he was asked to portray, and persuaded George Lucas to have him killed off. To this day, he throws away all his Star Wars-related fan mail unread.

His war/historical action film credits include: The Malta Story, The Bridge on the River Kwai, Tunes of Glory, HMS Defiant, Lawrence of Arabia, Dr. Zhivago, and Cromwell.