Born to a Jewish family Donath graduated from Vienna's Academy of Dramatic Art and became a prominent actor on the stage in Berlin. When Hitler came to power in 1933, he returned to Vienna and was active there in theater and film until the Anschluss in 1938. He began his American film career with Lady from Chungking (1942) and went on to appear in dozens of films, including Gilda (1946), The Jolson Story (1946), Jolson Sings Again (1949), The Great Caruso (1951), My Pal Gus (1952), Sirocco (1951), and Torn Curtain (1966).