According to The Hollywood Reporter, Ang Lee is also in talks to direct the action thriller, with Jerry Bruckheimer producing.
"Gemini Man" centers on an aging assassin who has to fight against his clone, who is 25 years younger and in his prime.
Back in 1997, the project was first set up at Disney as a pitch by Darren Lemke, while Don Murphy was set to produce the movie and Tony Scott was attached to direct.
The original concept was to have an actor such as Harrison Ford to play the older assassin and someone like Chris O'Donnell to play the younger one.
Skydance picked up the project in 2016, believing that technology nowadays has caught up to have someone like Smith, 48, playing two people with different ages who fight against each other.
Smith's deal, though, hasn't been done yet.