Warner Brothers have announced that the 41-year-old actor-director will star as a new incarnation of the Dark Knight in a film bringing Batman and Superman together.
The studio says Affleck will star opposite Henry Cavill, reprising his role as Superman from Man Of Steel.
The movie will also reunite Man Of Steel stars Amy Adams, Laurence Fishburne and Diane Lane.
The big-screen DC superhero mash-up was originally announced at last month’s Comic-Con International in San Diego by director Zack Snyder.
Snyder said in a statement that Affleck will provide a counter-balance to Cavill’s Superman.
Production is expected to begin in 2014, and the as-yet-untitled film is set for release on July 17, 2015.