Right-handed Robert Taylor spent weeks perfecting his ability to draw a gun with his left hand in preparation for this film. Ironically it was later revealed that the infamous photo of Billy the Kid with a gun in his left hand was mirrored and the famous outlaw was in fact right handed.
Maureen O'Sullivan was initially cast in the role of "Edith Keating" but left to be with her husband, director John Farrow, who was with the RCAF in Canada.
This film was first telecast in Los Angeles Monday 7 January 1957 on KTTV (Channel 11); it first aired in Philadelphia 22 March 1957 on WFIL (Channel 6), in Seattle 11 April 1957 on KING (Channel 5), in Hartford CT 23 April 1957 on WHCT (Channel 18), in Minneapolis 8 May 1957 on KMGM (Channel 9), in Tucson 3 June 1957 on KVOA (Channel 4), in Miami 12 July 1957 on WCKT (Channel 7), in Altoona PA 19 October 1957 on WFBG (Channel 10), in New York City 2 December 1957 on WCBS (Channel 2), in Chicago 8 January 1958 on WBBM (Channel 2), and in San Francisco 15 February 1958 on KGO (Channel 7). At this time, color broadcasting was in its infancy, limited to only a small number of high rated programs, primarily on NBC and NBC affiliated stations, so these film showings were all still in B&W. Viewers were not offered the opportunity to see these films in their original Technicolor until several years later.
Both Robert Taylor and Brian Donlevy were 10 years older than the real Billy the Kid and Pat Garrett were in 1880, the year Billy the Kid (1941) begins.
The birds Billy and Keating shoot at are animated.