Jason Reitman is directing the film starring Charlize Theron, according to The Hollywood Reporter.
The Mandate project centres on a writer of young adult fiction who returns to her Minnesota home to reunite with her married ex-boyfriend, who is also a new father.
Oswalt will play a self-loathing, crippled man who used to have a crush on Theron's character.
Wilson will play Theron's high school boyfriend.
Diablo Cody, who wrote the film's script, previously teamed up with Reitman on the Oscar-winning Juno.