Once a Thief was released in the US on 8 September 1965.
Zekial Marko adapted his 1961 novel Scratch a Thief (published under the name John Trinian) with his first screenplay (Marko also has a small role in the film, and was arrested during filming on charges unrelated to the film).
29-year-old Alain Delon had left France (where he was a huge star) to make films in Hollywood (Delon stated that he wanted to make a film a year in the US and one in Europe). While he had appeared in The Yellow Rolls-Royce (1964), Once a Thief was his first starring role in a Hollywood film.
24-year-old Ann-Margaret's success with Viva Las Vegas (1964) had been quickly overshadowed by the disappointments of Kitten with a Whip and The Pleasure Seekers (both 1964), and Once a Thief also failed to find an audience at the box office.
