The film centres on a woman (Haley Bennett), who hires a disparate group of gunslingers to protect her town from rampaging bandits that are led by a robber baron.
Bomer will star as the woman's husband, a man who tries to stand up to the robber baron, said The Hollywood Reporter.
Washington plays a bounty hunter, Pratt portrays a magician turned gambler, Vincent D'Onofrio stars as a mountain man, who used to be a killer, Wagner Moura will be seen as a caballero, Ethan Hawke as a sharpshooting war deserter and Jason Momoa as one of the villains.
It is scheduled for a release on January 13, 2017.