There have been numerous attempts to make a film version of Watchmen since 1986, when producers Lawrence Gordon and Joel Silver acquired film rights to the series for 20th Century Fox. Fox asked Alan Moore to write a screenplay based on his story, but he declined, so the studio enlisted screenwriter Sam Hamm. Hamm took the liberty of re-writing Watchmen's complicated ending into a "more manageable" conclusion involving an assassination and a time paradox. Fox put the project into turnaround in 1991, and the project was moved to Warner Bros., where Terry Gilliam was attached to direct and Charles McKeown to rewrite it. They used the character Rorschach's diary as a voice-over and restored scenes from the comic book that Hamm had removed. Gilliam and Silver were only able to raise $25 million for the film (a quarter of the necessary budget) because their previous films had gone over budget. Gilliam abandoned the project because he decided that Watchmen would have been unfilmable. "Reducing [the story] to a two or two-and-a-half hour film [...] seemed to me to take away the essence of what Watchmen is about," he said. After Warner Bros. dropped the project, Gordon invited Gilliam back to helm the film independently. The director again declined, believing that the comic book would be better directed as a five-hour miniseries.
In October 2001, Gordon partnered with Lloyd Levin and Universal Studios, hiring David Hayter to write and direct. Hayter and the producers left Universal due to creative differences, and Gordon and Levin expressed interest in setting up Watchmen at Revolution Studios. The project did not hold together at Revolution Studios and subsequently fell apart. In July 2004, it was announced Paramount Pictures would produce Watchmen, and they attached Darren Aronofsky to direct Hayter's script. Producers Gordon and Levin remained attached, collaborating with Aronofsky's producing partner, Eric Watson. Aronofsky left to focus on The Fountain and was replaced by Paul Greengrass. Ultimately, Paramount placed Watchmen in turnaround.
In October 2005, Gordon and Levin met with Warner Bros. to develop the film there again. Impressed with Zack Snyder's work on 300, Warner Bros. approached him to direct an adaptation of Watchmen. Screenwriter Alex Tse drew from his favorite elements of Hayter's script, but also returned it to the original Cold War setting of the Watchmen comic. Similar to his approach to 300, Snyder used the comic book panel-grid as a storyboard and opted to shoot the entire film using live-action sets instead of green screens. He extended the fight scenes, and added a subplot about energy resources to make the film more topical. Although he intended to stay faithful to the look of the characters in the comic, Snyder intended Nite Owl to look scarier, and made Ozymandias' armor into a parody of the rubber muscle suits from the 1997 superhero film Batman & Robin. After the trailer to the film premiered in July 2008, DC Comics president Paul Levitz said that the company had to print more than 900,000 copies of Watchmen trade collection to meet the additional demand for the book that the advertising campaign had generated, with the total annual print run expected to be over one million copies. While 20th Century Fox filed a lawsuit to block the film's release, the studios eventually settled, with Warner agreeing to give Fox 8.5 percent of the film's worldwide gross, including from sequels and spin-offs in return. The film was released to theaters in March 2009.
The Tales of the Black Freighter segments was adapted as a direct-to-video animated feature to be released that same month. Gerard Butler, who starred in 300, voices the Captain in the film. The film itself was released on DVD four months after Tales of the Black Freighter, and in November 2009, a four-disc set was released as the "Ultimate Cut" with the animated film edited back into the main picture. Len Wein, the comic's editor, wrote a video game prequel entitled Watchmen: The End Is Nigh.
Dave Gibbons became an adviser on Snyder's film, but Moore has refused to have his name attached to any film adaptations of his work. Moore has stated he has no interest in seeing Snyder's adaptation; he told Entertainment Weekly in 2008, "There are things that we did with Watchmen that could only work in a comic, and were indeed designed to show off things that other media can't". While Moore believes that David Hayter's screenplay was "as close as I could imagine anyone getting to Watchmen," he asserted he did not intend to see the film if it were made.
In 2008, Warner Bros. Entertainment released Watchmen Motion Comics, a series of narrated animations of the original comic book. The first chapter was released for purchase in the summer of 2008 on digital video stores, such as iTunes Store. A DVD compiling the full motion comic series was released in March 2009.