The Transformers actress is close to agreeing a deal to appear opposite Josh Brolin's disfigured gunslinger in DC Comics movie Hex. Her character Leila joins the eponymous bounty hunter to stop a Southern plantation owner (John Malkovich) from raising an army of the undead.
Production on Hex will begin this April with Jimmy Hayward directing.
In Fathom, meanwhile, Fox will portray Aspen, a young woman who discovers that she is a member of an underwater race with the ability to control water.
The 22-year-old became a fan of the Fathom comic when it was released in 1998. She has tracked down the movie rights to the property with producer Peter Safran, and will develop the adaptation with writer Jordan Mechner.