Officials announced the date and location Tuesday. The televised event will air on Paramount Network.
Bader (25-5) is the promotion's current light heavyweight champion, and advanced to the semifinals by knocking out Muhammed "King Mo" Lawal in just 15 seconds in May.
Fighting out of Gilbert, Arizona, Bader is 3-0 since signing with Bellator. He fought in the UFC from 2008 to 2016, but never made it to a championship fight.
Mitrione (13-5) is also a former UFC veteran, who has gone 4-0 since transferring to Bellator. He defeated Roy Nelson via majority decision in the opening round of the Grand Prix.