Ned Tanen spent years trying to acquire the rights to Eliot Ness's life story while at Universal, and finally set the project in motion after becoming head of production at Paramount, which owned the rights to Ness's memoir.

Producer Art Linson was not interested in adapting the 1959 ABC television series and instead wanted a more serious, authentic depiction of Ness's career, hiring playwright David Mamet to write an original screenplay.

Director Brian De Palma slightly rewrote some of Mamet's scenes during production to incorporate new locations, notably moving the homage to the Odessa Steps sequence from Battleship Potemkin from a hospital setting to Chicago Union Station.

De Palma initially wanted Don Johnson to play Eliot Ness, while Mickey Rourke, Jeff Bridges, William Hurt, Harrison Ford and Michael Douglas all turned down the role, and a 1985 Variety issue even announced Jack Nicholson as Ness before Kevin Costner was cast.

Kevin Costner met with former FBI agent and real-life Untouchable Al 'Wallpaper' Wolff at his home to research Ness's mannerisms and historical context.

Robert De Niro was De Palma's first choice for Al Capone, but his availability was uncertain due to a Broadway play, prompting De Palma to meet with Bob Hoskins as a backup; when De Niro became available, De Palma sent Hoskins a £20,000 check with a thank-you note, leading Hoskins to jokingly ask if there were other films he could be paid not to appear in.

Gene Hackman and Marlon Brando were also considered for Capone in case neither De Niro nor Hoskins could take the role.

To prepare for playing Capone, De Niro gained about 30 pounds, researched historical footage, and contacted Capone's original tailors to have identical suits and silk underwear made for him; he was paid $2 million for the role.

For the Canadian border shootout scene, Paramount had the Montana Film Commissioner's Office locate a period-appropriate bridge, settling on the Hardy Bridge near Cascade, Montana, which was closed to traffic for two weeks while crews built cabins, planted 600 trees brought in overnight, and cast 25 local residents as mounted Royal Canadian Mounted Police.

The Chicago Union Station shootout sequence is a deliberate homage to the Odessa Steps montage from Sergei Eisenstein's 1925 film Battleship Potemkin, and it was later parodied in Naked Gun 33 1/3: The Final Insult.

Despite winning the Academy Award for Best Supporting Actor for his role as Malone, Sean Connery was voted first place in a 2003 Empire poll for worst film accent due to his distinctly Scottish delivery of an Irish-American character.

An Untouchables prequel titled Capone Rising was developed with Brian De Palma returning to direct, with Nicolas Cage, Gerard Butler and Benicio del Toro all attached at different points to play a young Al Capone, though the film was ultimately never made.