Although he had already performed in various theater productions, Paul Stewart's career as an actor received a significant boost when he became a member of Orson Welles's Mercury Theater group in the mid-1930s. In 1938, he was the producer, writer, and studio announcer on Welles's infamous Halloween radio broadcast of "The War of the Worlds," a program that sent a significant portion of the American public into panic because they believed that earth was being attacked by Martians. Like many of the Mercury group, Stewart followed Welles out to Hollywood to make a career in the movies. He co-starred in Welles's ground-breaking cinematic debut, "Citizen Kane," playing newspaper mogul Kane's butler. More work followed, with many directors utilizing Stewart's taciturn, gruff demeanor to good effect in crime and war melodramas. After World War II, Stewart co-starred with Gregory Peck in the aerial combat film "Twelve O'Clock High," played a boxing manager opposite Kirk Douglas in the fight drama "Champion," and starred alongside Dana Andrews and Farley Granger in the film noir "Edge of Doom." He also acted with Humphrey Bogart in the hard-hitting crime film "Deadline - U.S.A.." Three of his most notable films during the 1950s were "Appointment with Danger," where he played a hitman, "The Bad and the Beautiful," reuniting with Kirk Douglas, and the brutal noir "Kiss Me Deadly" playing a venal criminal. In the mid-1950s, Stewart began directing for television, as well as continuing to work as an actor.