The mixed martial artist will portray one of the villainous Red Mist's henchmen in Jeff Wadlow's superhero sequel.
The new broke when Liddell was spotted with John Leguizamo on the movie's set at Pinewood Studios and was later confirmed over Twitter by his management.
Kick-Ass 2 sees Aaron Taylor-Johnson, Christopher Mintz-Plasse, Chloë Moretz and Nicolas Cage reprise their roles from the original, alongside series newcomers Jim Carrey, Donald Faison and Leguizamo.
The movie will be based on two comic book series written by Mark Millar - Hit-Girl and Kick-Ass 2 - with the former serving as the first half-hour of the film.
Kick-Ass 2 is scheduled to be released on June 28, 2013 in the US and on July 19, 2013 in the UK.
Watch the trailer for Matthew Vaughn's original Kick-Ass film below: