Said to take place within the elite New York fashion scene, the film will allegedly run in the vein of Darren Aronofky's Black Swan.
The 28-year-old will produce through her July Moon production company in partnership with 21 Laps' Shawn Levy and Dan Cohen, with STX to oversee the project. The script has been penned by newcomer Michael Paisley, with a director yet to be confirmed.
STX chairman Adam Fogelson expressed the team's excitement over scoring Gomez for the film.
"Selena's involvement is an exciting direction for this project. She is supremely talented as both a star and a producer," he said.
"Teaming with Selena with Shawn and Dan's expertise in the horror-thriller genre will elevate [the film] and couldn't be more thrilled by the way this is being developed."
Gomez has served as an executive producer on the rom-com Broken Hearts Gallery, which starred Australians Dacre Montgomery and Geraldine Viswanathan, as well as the documentary Living Undocumented and Netflix's 13 Reasons Why.
This would be her first role in a horror film, not including her part in the 2019 horror-comedy The Dead Don't Die.