Caragh M. O'Brien is an American novelist, best known as the author of the Birthmarked trilogy, a series of young adult, dystopian novels. Her books are set in a world destroyed by climate change. She has also written an adult novel, Annie Bot, about a malfunctioning gynoid companion, under the pen name Sierra Greer.

Born in St. Paul, Minnesota, Ms. O'Brien earned her BA from Williams College and her MA from Johns Hopkins University. Once a high school English teacher, she resigned to write young adult novels full-time.