As a youth, Jason ran away from home, worked as a bank clerk and, after stage training in Vienna, made his acting debut in Zurich. He remained unknown, traveling for several years and acting in Germany, Austria and Switzerland, until Fritz Lang cast him as the psychopathic child killer in M (1931). After several more films in Germany, Jason left as the Nazis came to power, going to Paris, London and, in 1935, Hollywood. He played Raskolnikov in Crime and Punishment (1935) and a series of Mr. Moto movies during the late 1930s. He began his pairing with Sydney Greenstreet as Joel Cairo in The Maltese Falcon (1941), continued in Casablanca (1942) and seven other films during the early 1940s. In Germany he wrote, directed and starred in Der Verlorene (1951). After that, somewhat heavier, he played in a string of not-so-stellar efforts, one exception being his role as a clown in The Big Circus (1959).