Mark Millar (; born 24 December 1969) is a Scottish comic book writer, best known for his work on The Authority, The Ultimates, Marvel Knights Spider-Man, Ultimate Fantastic Four, Civil War, Kingsman: The Secret Service, Wanted, Chrononauts, Superior and Kick-Ass, the latter seven of which have been, or are planned to be, adapted into feature films.

His DC Comics work includes Superman: Red Son. At Marvel Comics he created The Ultimates, selected by Time magazine as the comic book of the decade, and described by screenwriter Zak Penn as a major inspiration for The Avengers movie. Millar also created Wolverine: Old Man Logan and Civil War, two of Marvel's biggest-selling graphic novels. Civil War (comics) was the basis for the Captain America: Civil War film and Old Man Logan was the inspiration for Fox's Logan film.

Millar has been an executive producer on all of his films, and for four years worked as a creative consultant to Fox Studios on their Marvel slate of films. In 2017, Netflix bought Millar's comic line, Millarworld, which Millar and his wife Lucy will continue to run; publishing new comics and adapting them for other media.