Nielsen was born on 11 February 1926 in Regina, Saskatchewan. His mother, Mabel Elizabeth (nee Davies), was an immigrant from Wales, and his father, Ingvard Eversen Nielsen, was a Danish-born constable in the Royal Canadian Mounted Police. Nielsen had two brothers; the elder, Erik Nielsen (1924-2008), was a long-time Canadian Member of Parliament, cabinet minister, and Deputy Prime Minister of Canada from 1984 to 1986. Nielsen's half-uncle Jean Hersholt was an actor known for his portrayal of Dr. Christian in a radio series of that name, and the subsequent television series and films.

After Airplane! and The Naked Gun, Nielsen portrayed similarly styled roles in a number of other films. These mostly emulated the style of The Naked Gun with varying success and often targeted specific films; many were panned by critics and most performed poorly. Repossessed (1990) and 2001: A Space Travesty (2001) were parodies of The Exorcist and 2001: A Space Odyssey, respectively. Both attempted absurd comedy, but were poorly received. Even a leading role in a Mel Brooks comic horror, Dracula: Dead and Loving It, failed to generate much box-office excitement, although it did gain a following in a later release to video. Both 1996's Spy Hard and 1998's Wrongfully Accused, a parody of James Bond films and The Fugitive, were popular on video, but not well received by critics. His attempt at children's comedies met additional criticism. Surf Ninjas (1993) and Mr. Magoo (1997) had scathing reviews. Several critics were disappointed that Nielsen's role in Surf Ninjas was only "an extended cameo" and Chris Hicks recommended that viewers "avoid any comedy that features Leslie Nielsen outside of the Naked Gun series." Jeff Miller of the Houston Chronicle panned Mr. Magoo, a live-action remake of the 1950s cartoon, by saying, "I'm supposed to suggest how the film might be better, but I can't think of anything to say other than to make the film again." Nielsen's first major success since The Naked Gun came in a supporting role in Scary Movie 3 (2003). His appearance as President Harris led to a second appearance in its sequel, Scary Movie 4 (2006). This was the first time Nielsen had reprised a character since Frank Drebin. In one scene, Nielsen appeared almost nude, and one critic referred to the scene as putting "the 'scary' in Scary Movie 4."

which other movie was a fail?
His attempt at children's comedies met additional criticism. Surf Ninjas (1993) and Mr. Magoo (1997) had scathing reviews.