M premiered in Berlin on 11 May 1931 at the UFA-Palast am Zoo in a version lasting 117 minutes. The original negative is preserved at the Federal Film Archive in a 96-minute version. In 1960, an edited 98-minute version was released. The film was restored in 2000 by the Netherlands Film Museum in collaboration with the Federal Film Archive, the Cinemateque Suisse, Kirsch Media and ZDF/ARTE., with Janus Films releasing the 109-minute version as part of its Criterion Collection using prints from the same period from the Cinemateque Suisse and the Netherlands Film Museum. A complete print of the English version and selected scenes from the French version were included in the 2010 Criterion Collection releases of the film.
M was later released in the U.S. in 1933 by Foremco Pictures. After playing in German with English subtitles for two weeks, it was pulled from theaters and replaced by an English version. The re-dubbing was directed by Eric Hakim and Lorre was one of the few cast members to reprise his role in the film. As with many other early talkies from the years 1930–1931, M was partially reshot with actors (including Lorre) performing dialogue in other languages for foreign markets after the German original was completed, apparently without Lang's involvement. An English-language version was filmed and released in 1932 from an edited script with Lorre speaking his own words, his first English part. An edited French version was also released but despite the fact that Lorre spoke French his speaking parts were dubbed.
A Variety review said that the film was "a little too long. Without spoiling the effect—even bettering it—cutting could be done. There are a few repetitions and a few slow scenes." Graham Greene compared the film to "looking through the eye-piece of a microscope, through which the tangled mind is exposed, laid flat on the slide: love and lust; nobility and perversity, hatred of itself and despair jumping at you from the jelly".
In 2013 a DCP version was released by Kino Lorber and played theatrically in North America in the original aspect ratio of 1.19:1. Critic Kenneth Turan of the Los Angeles Times called this the "most-complete-ever version" at 111 minutes. The film was restored by TLEFilms Film Restoration & Preservation Services (Berlin) in association with Archives françaises du film - CNC (Paris) and PostFactory GmbH (Berlin).