Jenkins, 46, and Johns, 44, have been working on the script for quite some time and now Callaham will help them finish it, according to The Hollywood Reporter.
Jenkins and Callaham, 39, have previously worked together on "Jackpot", an English-language adaptation of Jo Nesbo's book. The project was set to be Jenkins' next movie before she took on the task to direct "Wonder Woman".
Though the storyline for the Gal Gadot starrer's sequel is being kept under wraps, Jenkins has said she wants to jump ahead by several decades from the first film, set in Europe during World War I.