Errol Flynn did all of his own boxing stunts in the film, and although production was shut down for a time after Flynn suffered a mild heart attack, he came back and finished the picture without ever using a double.
Soon after completing "Gentleman Jim," Flynn became embroiled in an infamous rape trial. During screenings of "Gentleman Jim," his closing line of "I'm no gentleman" was met with laughter and derision. The line was cut from the conclusion of the 1944 radio broadcast.
Arthur Shields (Father Burke) and John Loder (Carlton De Witt) fought on opposite sides of the Easter Rising of 1916: Shields fought with the Irish republicans while Loder was a second lieutenant in the British Army. Furthermore, Loder was the son of General William Lowe, the British officer to whom Pádraig Pearse surrendered on April 29, 1916. Shields had previously played Pearse in The Plough and the Stars (1936).
This film's first documented telecasts took place in Phoenix Thursday 26 July 1956 on KVAR (Channel 12), in Cincinnati Saturday 28 July 1956 on WKRC (Channel 12), in Tucson Monday 30 July 1956 on KDWI (Channel 9), in Bellingham WA Friday 7 September 1956 on KVOS (Channel 12), in San Francisco Friday 12 October 1956 on KRON (Channel 4), in Bloomington IN Wednesday 14 November 1956 on WTTV (Channel 4), and in Portland OR Saturday 17 November 1956 on KOIN (Channel 6).