The film's casino set was the most expensive set constructed in Hollywood since the end of the war. The set comprised 14 gaming rooms featuring $50,000 worth of Las Vegas gambling equipment that was shipped to Hollywood.
On 12 May 1947, the "Lux Radio Theater" presented a radio version of this story. Dick Powell and Lee J. Cobb reprised their roles for the live radio broadcast.
When Lee. J. Cobb (Inspector Koch) was called before the House UnAmerican Activities Committee in 1953 and given a chance to clear his name by naming communists he had known, Cobb named Shimen Ruskin who plays the dry-cleaner in this film.
On August 16, 1977, "Johnny O'Clock" was being televised on KTVU Channel 2's "Dialing For Dollars" (Oakland-San Francisco CA) when word of Elvis Presley's death interrupted the broadcast.
Actor Lee J. Cobb was borrowed from Twentieth Century-Fox, actor S. Thomas Gomez was borrowed from Universal, and film editor Warren Low was borrowed from Hal Wallis Productions for this feature film.