Hart was born on October 24, 1904, in Bronx, New York. He was the son of Barnett Hart, who was born in Great Britain and worked as a cigar maker, and Lillian (nee Solomon) Hart. Hart grew up in poverty after the advent of the cigar rolling machine made his father's profession outdated. When Hart left school in his mid-teens, he was already a confirmed fan of the theater. He got a job as a clerk to a theater producer, Augustus Pitou, Jr., and wrote a script for him, submitted under a pseudonym. The previews of The Hold-Up Man or The Beloved Bandit were awful, and Hart was fired.

While spending several years directing small theater groups and working as a social director at resorts during the summer, Hart continued to write plays, turning out one per year, none of which were produced until he got a break...