Zero was born to parents Israel Mostel, an Eastern European Jew, and Cina "Celia" Druchs, also from a Jewish family. His mother was born in Poland and grew up in Vienna.
Zero's father immigrated to the USA in 1989 and his mother in 1908. They met in the States and married there. Zero's father had four children from his previous marriage and he had an additional four children with Cina. Zero was his fathers seventh child.
At the beginning his family lived in Brooklyn. From there they moved to Moodus, Connecticut, where they bought a farm. As the farm proved to be unsuccesful the family moved to the lower east side of Manhattan, where Zero went to public school.
Zero passed away from a cardiac arrest in Philadelphia , he was performing in a pre-broadway production of The Merchant. His career began in nightclubs and radio. His Broadway debut was in 1942 in Keep Em Laughing. He was married to former dancer Kathryn Harkin. Zero has two sons Tobias and actor Josh Mostel.