In the film, Smith (Owen), a drifter and former black-ops soldier, rescues a newborn from being killed by assassin Hertz (Giamatti) and his henchmen.

According to Davis, the film's idea came after he saw a gun-battle scene from Hard Boiled in which Chow Yun-fat rescues newborn babies from gangsters.

In a rough part of town, Smith, a carrot-eating drifter and ex-black-ops soldier, sees a pregnant woman fleeing a hitman.

Struggling to use his gun, Smith places live bullets between his broken fingers and detonates them with a fireplace, critically wounding Hertz.

[5][6] Smith's misanthropy derived from writer-director Michael Davis' frustration when his 1989 script about Alfred Kinsey failed to materialize as a feature film.

[7] His research about Kinsey and human sexuality in general inspired the character of Donna Quintano, a gold-hearted prostitute and Smith's eventual love interest.

[12][13] By 2000, Davis had begun writing the screenplay;[11] when the script was finished, however, studios refused to get it made after the Columbine High School massacre happened, causing him to shelve the project and return to making low-budget independent films.

[14] During his subsequent years as an independent filmmaker, Davis started putting together an animatic of the script's action scenes using a Wacom tablet and the iMovie app.

[11] The role of Donna went to Monica Bellucci, who liked the script and the character: an independent woman who "does dangerous, dark dirty things in a playful way".

[3] Principal photography took place in Toronto and lasted fifty-five days,[4][11] with Hong Kong's Peter Pau serving as cinematographer.

The campaign included a viral video and a website selling bogus items ranging from bulletproof strollers to riot helmets for infants.

The hoax campaign was taken seriously by global media and the blogging community;[24][25] Aftonbladet, Sweden's largest evening tabloid, carried the story on its online edition for some time.

[32] The film's DVD and Blu-ray versions were released in January 2008 by New Line Home Entertainment with a BTS featurette titled "Ballet of Bullets", 17 minutes of animatics and audio commentary from director Michael Davis, trailers and deleted scenes.

"[39] Roger Ebert for the Chicago Sun-Times scored the film 3⁠1/2⁠ out of 4 stars, comparing it favorably with Sin City as "the most audacious, implausible, cheerfully offensive, hyperactive action picture [he had] seen".

[8] Frank Scheck in The Hollywood Reporter called it a "ramped-up action movie on steroids" that "makes Hard Boiled look restrained".

[40] Ebert extended his praise toward the film's acting, calling Owen's character sympathetic and Giamatti's "surprisingly, teeth-gnashingly evil".

[8] Scheck complimented Owen's "low-rent James Bond" performance, and was delighted to see Giamatti cast against his usual "nerdy" on-screen persona.

[40] A. O. Scott gave the film a scathing review for The New York Times, calling it "a worthless piece of garbage" and that it was one of several "witless, soulless, heartless movies that mistake noise for bravura and tastelessness for wit".

"[41] James Berardinelli gave the film a mixed review, saying that while it delivered gunfights as advertised, he complained that it "pretty much consists of shoot-outs and chases overtaking each other like waves rolling onto a beach, each more over-the-top than its predecessor".

Berardinelli scored the film 2.5 out of 4 stars, writing that he "like[d] the audacity and its willingness to push the envelope beyond the limits of good taste.

In the end, it's a little too long and uneven to recommend outright, but [he] won't deny having enjoyed aspects of what Davis is offering.

"[42] In 2016, Shoot 'Em Up made the list of "25 great action films that are 90 minutes or under" compiled by Nick Horton of Den of Geek.