Gentleman Jim follows Errol Flynn as James J. Corbett, a brash young bank teller who becomes a professional boxer and rises to fame under the guidance of British coach Harry Watson. With his innovative footwork and limitless self-confidence, Corbett wins several matches and eventually challenges heavyweight champion John L. Sullivan, ultimately emerging victorious and becoming the new champion. Along the way, he also captures the heart of socialite Victoria Ware, played by Alexis Smith.