Born Trevor Wallace Howard-Smith in Cliftonville, Kent, he attended the Royal Academy of Dramatic Art and acted on the London stage for several years before World War II. His first major role was in Brief Encounter in 1945, and starred in The Third Man and Sons and Lovers, for which he was nominated for an Academy Award for Best Actor.
Howard later appeared in such films as Mutiny on the Bounty, The Charge of the Light Brigade, Mary, Queen of Scots, Pope Joan, Ludwig, A Doll's House and Ryan's Daughter.