His acting quality, usually playing a powerful character, such as the lead in Scarface (1932), was partly a result of his intense preparation for his parts, often immersing himself in study of the real character's traits and mannerisms. He was also highly skilled in using makeup techniques, a talent he learned from his parents, who were also actors, and from his early years on stage with the Yiddish Theater in Chicago. At the age of 12, he played the stage role of an 80-year-old man; in one of his films, Seven Faces, he played seven different characters.
He made 25 films and won the Academy Award for Best Actor for his role in the 1936 film The Story of Louis Pasteur. He also starred in numerous Broadway plays and won the Tony Award for Best Actor in a Play for his role in the 1955 production of Inherit the Wind.