Cast of Kick-Ass

Aaron Johnson as David "Dave" Lizewski / Kick-Ass: Johnson said that Kick-Ass is a "sensitive guy" who lost his mother and is a "nobody" at school, so he creates his superhero identity "as this whole different persona." Johnson said that Dave is "a kid who’s got the guts to go out there and do something different. Christopher Mintz-Plasse originally auditioned for the role of Kick-Ass, but during the audition the producers believed that his acting was too loud and obnoxious for the lead, so they immediately gave Mintz-Plasse the role of Red Mist instead.

Nicolas Cage as Damon Macready / Big Daddy: Vaughn described Cage's performance as a little bit Elvis and a little bit Adam West. A character in the film even says his costume looks like that of Batman. Cage was inspired by his costume to try delivering his lines in the same style Adam West used for Batman. The police officer father of an ex-girlfriend also influenced his performance; the habit of Big Daddy referring to Hit-Girl as "child" stems from the police officer.

Chloë Grace Moretz as Mindy Macready / Hit-Girl: Vaughn commented on the maturity of Moretz, who said that because she has four older brothers, she was no stranger to much of the language in the script. Her mother read the script and permitted her to use the profanity in the movie. Jane Goldman, one of the two co-writers of the script, said, "We just really wanted Hit-Girl to be a character who, in a sense, simply happens to be an eleven-year-old girl, in the same way that Ripley in Alien could have been a guy but the part happened to be played by Sigourney Weaver." Goldman said that Mindy "is genuinely dangerous, she's genuinely mad. It's not her fault: she's been raised in this environment where she doesn't know anything different. She's unwittingly part of a folie a deux."

Christopher Mintz-Plasse as Chris D'Amico / Red Mist: Frank D'Amico's son. Millar said that "the idea was that he was going to be a more minor character in the first film. Then we saw what Christopher Mintz-Plasse was capable of! [...] So the idea of McLovin' and the fun Red Mist doing something horrible is genuinely quite disturbing when you see it happen. We couldn't have got away with that with another actor. The minute we saw his performance, we were looking at each other and realised how good he was and what we could do with him in the future...." Mintz-Plasse said that when he first wore the Red Mist costume, he felt that it was entertaining and that he "looked so bad-ass." The actor sent photographs of himself in costume to his friends. Three weeks into the filming, Mintz-Plasse decided that the costume was not very comfortable and "a big pain in the ass." Mintz-Plasse wore the costume for 12 hours per filming day. Mintz-Plasse had to learn how to use a stick-shift in order to drive the Ford Mustang that is used in the film. Vaughn told Mintz-Plasse that the actor would have to pay for the car if he crashed it.

Mark Strong as Frank D'Amico: The head of a criminal organization. Strong says he is drawn to playing the antagonist. He tries to "understand the purpose of the character", and then work on building a believable individual.

Lyndsy Fonseca as Katie Deauxma: Dave's longtime crush and eventual girlfriend.

Michael Rispoli as Big Joe

Kofi Natei as Rasul: A gang leader whom Dave (as Kick-Ass) challenges until Hit-Girl arrives to kill the gang members.

Katrena Rochell as Female Junkie

Yancy Butler as Angie D'Amico: Frank's wife and Chris' mother.

Jason Flemyng as Lobby Goon: The building doorman.

Elizabeth McGovern as Alice Lizewski, Dave's mother.

Garrett M. Brown as James Lizewski, Dave's father.

Sophie Wu as Erika Cho: Katie's best friend.

Dexter Fletcher as Cody

Clark Duke and Evan Peters as Marty Eisenberg and Todd Haynes: Dave's two best friends.

Xander Berkeley as Detective Victor "Vic" Gigante: A police officer working for D'Amico.

Omari Hardwick as Sergeant Marcus Williams: Former partner of Damon Macready.

Deborah Twiss as Mrs. Zane: Dave's English teacher.

Craig Ferguson as Himself

John Romita, Jr. as Atomic Comics barista