The 42-year-old actor teased his involvement with the DC Comics movie in July, and announced the role Wednesday on Twitter.
"'Kneel at his feet or get crushed by his boot,'" Johnson quoted. "My honor to become... #BlackAdam #TheAntiHero #DCComics."
In the comics, Black Adam is the primary adversary of superhero Billy Batson, or Shazam. The character was originally depicted as an ancient Egyptian prince and villainous predecessor to the hero, but later stories saw him become an antihero figure. The wizard Shazam granted the same powers to Black Adam and Billy Batson, and both men receive superhuman strength, stamina and speed when they say the sorcerer's name.
The film adaptation is in the works at New Line Cinema, and Jack the Giant Slayer writer Darren Lemke will pen the script. Johnson and Hiram Garcia will produce.
"We love Dwayne and have had nothing but success with him over the years," New Line President Toby Emmerich said in a statement. "When I look at Dwayne both off screen and on screen, he is such a larger than life character and it just made perfect sense that we put him in a DC comic movie. You look at these comic book characters and they have this certain swag and charisma that Dwayne carries with him where ever he is so that's why this always made sense."
Johnson last appeared in Hercules, and is scheduled for Fast & Furious 7 in 2015.