Joseph Bromberg was born in Timisoara, part of the Austria-Hungarian Empire, on 25 December, 1903. The family moved to the United States in 1908 and settled in New York City. After graduating from Stuyvesant High School, he had acting lessons with Leo Bulgakov, who had a student with Constantin Stanislavski.
Bromberg eventually joined the Group Theatre in New York led by Lee Strasberg. Members of the group tended to hold left-wing political views and wanted to produce plays that dealt with important social issues. Bromberg joined the American Communist Party and in 1935 appeared in Waiting for Lefty, a play by a fellow party member, Clifford Odets. Another member,