Joseph Stein was born in New York City to Jewish parents, Charles and Emma (Rosenblum) Stein, who had immigrated from Poland, Stein grew up in the Bronx. He graduated in 1935 from CCNY, with a B.S. degree, then earned a Master of Social Work degree from Columbia University in 1937. He began his career as a psychiatric social worker from 1939 until 1945, while writing comedy on the side.