James McAvoy screentested for the lead role in early 2006, but was initially rejected, as the studio wanted a more "conventional" leading man. He was later recalled, when the producers decided that his character was more "the runt of the litter". The studio ultimately changed its mind, and wanted someone geeky. McAvoy got the part.
While on location in Chicago, The Dark Knight (2008) was the neighboring film production, in which Morgan Freeman worked while shooting this film. On one occasion, Mark Millar, the creator, snuck onto the neighboring set, to see the Batpod, which was used for filming. He was evicted from the set, when security and Producer Lauren Shuler Donner (who visited the set as well) caught him in the act.
In the office at the end of the film a nameplate is visible on one of the cubicle walls. The nameplate reads "J.G Millar" which is a composite of writer Mark Millar and artist J.G. Jones, on whose comic the film is based.
Angelina Jolie was coming out of her pregnancy, and A Mighty Heart (2007), and wanted to make an action film. Ian Livingston, President of Eidos at the time, confirmed that there were talks with Paramount to make a third Tomb Raider movie. The movie had to be shot and be released by the end of 2007, due to Paramount's contract. That was impossible, so the plans were scrapped. Angelina Jolie decided to film this movie, and she personally picked the Lara Croft Tomb Raider: The Cradle of Life (2003) writer to tailor the role of Fox for her, and completely re-shape the film to her likes.
The first film to use Red Digital Cinema's Red One digital cameras. Several prototypes were used, alongside film cameras, to shoot about ten scenes. However, no Red One footage appears in the final cut of the film.
The script went through several revisions, with the most significant one being the third act that was re-written by Chris Morgan in mid-2006. The first draft was rejected by Mark Millar, because he felt the script was too tame and Americanized. Dean Georgaris also contributed a re-write, and tailored the role of The Fox specially for Angelina Jolie. Finally, original writers Derek Haas and Michael Brandt then put in the final re-write to even out the voice of Wesley, which was established in the first draft.
James McAvoy would go on to play young Professor Charles Xavier in the X-Men franchise, Chris Pratt would go on to play Peter Quill a.k.a. Star Lord in the Marvel Cinematic Universe, and Morgan Freeman played Lucius Fox in the Dark Knight trilogy.
Screenwriters Michael Brandt and Derek Haas named several of the movie's characters after people from their college alma mater, Baylor University. Robert Darden, the name of Wesley's first target for assassination, is the writing professor in whose class they first met. They have used the name Darden for the first victim in several other films, as well: 3:10 to Yuma (2007) and 2 Fast 2 Furious (2003). Sloan, the character played by Morgan Freeman, is taken from the University's previous President, who was forced to step down under pressure from faculty and alumni.
About 53 minutes into movie, Morgan Freeman's character decodes names from the woven fabric's yarn as strings of zeros and ones. This is actually ASCII code used in computers and electronic data processing. In ASCII, capital A is represented by numeric value 65, which is written in 8-bit binary number system 01000001, B has ASCII value 66, C has 67 and so on.
Vehicles featured include a Dodge Viper SRT-10; 1966 Ford Mustang; Chevrolet Corvette [C4]; the police cars were Ford Crown Victorias and a 2000 Chevrolet Impala 9C1; elevated subway trains; garbage truck; a Chevrolet Step Van; an express train; and a 1971 VAZ 2101 Zhiguli.
On Dec 16, 2014, the amalgam british band McBusted made a video for their song Get Over It, with the intro of the video influenced by the movie's first act with Tom Fletcher hitting his boss' face with a keyboard as Wesley.
The graphic novel that inspired the movie is actually about super-villains who took over the world and defeated almost every super-hero. The movie took a less fantastic/supernatural approach, and some characters were not used such as Shithead, a monster made with the feces of 666 of the most evil people on Earth, including Hitler.
At the beginning of the movie, Wesley walks outside of his apartment and looks up to see Cross' house. To the left of it, is a telephone pole with a flyer that says "Your Father's" revealing that Cross is Wesley's real father.
In the final library scene, Fox decides to follow the code, and the bullet she shoots has the word 'Goodbye' engraved on it. You can see the word clearly just prior to it entering the first assassin's head.
In the scene where Sloan (Morgan Freeman) reveals that Wesley (James McAvoy) is staying in his father's room, he picks up a picture, and it reveals that Cross is in picture with Sloan, and the man who is not his father, who Wesley assumes to be.
During the conversation between Wesley and the Priest, he explains to Wesley that his father (Cross) did not want to hurt him or get him involved with the Fraternity. Throughout the movie, each gunfight with Cross will show that every bullet fired from his gun was aimed at either Fox or an active member of the Fraternity. The only time Cross shot Wesley was during the chase, in particular, when Mole was shot unintentionally by Wesley. The only reason Cross did this deed, other than to lure him closer to his son, was to save his life. Mole was K.I.A. by Wesley, the targets son, so if Cross had not shot him, Wesley may be suspected and killed by the Fraternity rather than the idea of Cross trying to kill them all during pursuit.
In James McAvoy's earlier film Strings (2004), McAvoy's character in that film Hal Tara sets out to avenge his father whom has been murdered, only to discover that it his father was not murdered and had committed suicide. The same things happens to Wesley Gibson in this film. Wesley joins The Fraternity so he can avenge his father whom was killed by Cross. But, Wesley soon discovers that his deceased father was not his deceased father, but Cross himself.