Trevor was born Claire Wemlinger. After attending Columbia and the American Academy of Dramatic Arts, she began her acting career in the late '20s in stock. By 1932 she was starring on Broadway; that same year she began appearing in Brooklyn-filmed Vitaphone shorts. She debuted onscreen in feature films in 1933 and soon became typecast as a gang moll, a saloon girl, or some other kind of hard-boiled, but warm-hearted floozy.