Screenwriter Brian Helgeland was a longtime fan of Ellroy's novels and lobbied for years to script the film after Warner Bros. acquired the rights in 1990, but the studio initially wanted only well-known screenwriters, and a meeting he finally secured was canceled two days before it was to occur.

Director Curtis Hanson and Helgeland worked on the script together for two years, condensing the novel's eight plotlines down to three and focusing only on scenes involving the three main cops; Helgeland wrote seven drafts for free while Hanson turned down other jobs.

To convince New Regency owner Arnon Milchan to finance the film, Hanson prepared a presentation of 15 vintage postcards and photographs of 1950s Los Angeles, including images symbolizing prosperity as well as darker elements like the scandal magazine Confidential and a mugshot of Robert Mitchum after his marijuana bust.

Arnon Milchan was initially against casting 'two Australians' in the lead roles; Guy Pearce later wryly noted that he was actually born in England to a New Zealand father, while Russell Crowe, a Māori, is a New Zealander.

Hanson deliberately avoided watching Guy Pearce in The Adventures of Priscilla, Queen of the Desert before casting him, fearing it might influence his decision about the actor for the role of Ed Exley.

Hanson told Kevin Spacey to think of Dean Martin while playing Jack Vincennes, casting the actor deliberately against type to capture a 'movie star among cops' persona.

Simon Baker, later known for The Mentalist, played the small role of Matt Reynolds and was billed as Simon Baker Denny in the film's credits.

Before filming, Hanson brought Russell Crowe and Guy Pearce to Los Angeles for two months to immerse them in the city and era, provided dialect coaches, screened vintage police training films, and introduced them to real police officers for research.

Cinematographer Dante Spinotti suggested shooting in the Super 35 widescreen format with spherical lenses to give the film the feel of a still photograph, inspired by Robert Frank's 1958 photo book The Americans.

The house used for Lynn Bracken's home at 501 Wilcox Avenue required a $75,000 renovation to transform it into the Spanish-style home described in the script, while Pierce Patchett's home is the real-life Lovell House designed by Richard Neutra.

The Victory Motel was one of the few purpose-built sets for the film, constructed on a flat stretch of the Inglewood Oil Field in Culver City.

Warner Bros. reportedly did not want the film shown at the Cannes Film Festival due to a perceived anti-studio bias there, so Hanson and other producers bypassed the studio and sent a print directly to the festival's selection committee, which loved it.

L.A. Confidential is one of only four films in history to sweep the 'Big Four' critics' awards (National Society of Film Critics, New York Film Critics Circle, Los Angeles Film Critics Association, and National Board of Review), alongside Schindler's List, The Social Network, and One Battle After Another.

A proposed sequel set in 1974, with Russell Crowe and Guy Pearce reprising their roles and Chadwick Boseman playing a young cop named James Muncie, was in development before Boseman's death; the project later failed to attract studio interest, with Netflix executives reportedly falling asleep during the pitch.