Mark Fergus is a screenwriter, working alongside his writing partner, Hawk Ostby. They are best known for their work on Children of Men (for which they were nominated for the Academy Award for Best Adapted Screenplay) and Iron Man. Their other work includes First Snow, which was also directed by Fergus, and Cowboys & Aliens.

They are the creators and executive producers of the TV series The Expanse, which debuted on Syfy in December 2015 and ended its six-season run on Amazon Prime Video on January 14, 2022.