Balsam made his film debut with an uncredited role in "On the Waterfront" (1954), directed by his Actors' Studio colleague Elia Kazan. Balsam played an official of the New York Port Authority investigating mob involvement in the city's waterfront unions. His breakthrough role came a few years later, when he played Juror #1 in "12 Angry Men" (1957). He would collaborate with the film's director, Sidney Lumet, twice more with "The Anderson Tapes" (1971) and "Murder on the Orient Express" (1974).