Kinnaman has won the role of Lancelot and is now in final negotiations to join the film's cast, according to The Hollywood Reporter.
The studio has yet to decide on an actor to portray Arthur, although Kit Harington, Sam Claflin and Dominic Cooper have all been linked to the role.
Kinnaman is best known for playing the male lead in AMC's critically acclaimed crime series The Killing.
Arthur & Lancelot will be directed by David Dobkin, who also wrote the movie's script.
> The Killing star Joel Kinnaman joins Safe House