The screenplay by David Webb Peoples dates back to 1976, when the project was developed under the titles 'The Cut-Whore Killings' and 'The William Munny Killings'. It was originally optioned by Francis Ford Coppola, who failed to raise enough money to develop it further.

Clint Eastwood received the script in the early 1980s but deliberately waited years before making it, feeling he should do other projects first.

In 1984, Eastwood's longtime story editor Sonia Chernus sent him a scathing memo about the script, calling it 'an insult to this company' and urging him to 'get rid of it FAST'.

Eastwood personally called Richard Harris to offer him the role of English Bob while Harris happened to be watching Eastwood's 1973 film High Plains Drifter, which made Harris initially think the call was a prank.

Gene Hackman was initially reluctant to take the role of Little Bill Daggett because his daughters were upset he kept starring in violent films, but his agent and Eastwood convinced him to accept.

Filming took place between August 26 and November 12, 1991, with much of the shoot occurring in Alberta, Canada, in August 1991 under director of photography Jack Green.

Production designer Henry Bumstead, who had previously worked with Eastwood on High Plains Drifter, was hired to create the film's deliberately 'drained, wintry look'.

The railroad scenes were filmed on the historic Sierra Railroad in Tuolumne County, California.

Eastwood dedicated the film at the end of the credits to his mentors Sergio Leone and Don Siegel, with the message 'Dedicated to Sergio and Don'.

The film's trailer music was composed by Randy J. Shams and Tim Stithem in 1992, while the main theme, 'Claudia's Theme', was composed by Clint Eastwood himself.

A 2013 Japanese remake directed by Lee Sang-il and starring Ken Watanabe transposed the story to Japan during the Meiji period, replacing the outlaw protagonist with a samurai.

Unforgiven's $15 million opening weekend was the best-ever opening for a Clint Eastwood film at the time and set a record for the highest August opening weekend, until it was surpassed a year later by The Fugitive.

In 2006, the Writers Guild of America ranked David Webb Peoples' screenplay for Unforgiven as the 30th-greatest ever written.

In 2004, Unforgiven was selected for preservation in the United States National Film Registry by the Library of Congress for being 'culturally, historically, or aesthetically significant'.