Margaret Haddix was born near Washington Court House, Ohio, where she grew up on a farm.

She received a Bachelor of Arts in creative writing and journalism from Miami University in 1987. She worked as a newspaper copy editor in Fort Wayne, Indiana; as a newspaper reporter in Indianapolis; and as a community college instructor and freelance writer in Danville, Illinois. Haddix and her husband, Doug, a newspaper editor, now live in Columbus, Ohio, with their two children.

In 2004, Haddix and her publishers, Simon & Schuster, threatened to sue the makers of M. Night Shyamalan's film The Village over alleged similarities with the plotline of her first novel Running Out of Time. The filmmakers wrote off the similarities as "meritless".

Haddix has received the International Reading Association Children's Book Award, the American Library Association Best Book for Young Adults Award, and the Quick Pick for Reluctant Young Adult Readers citations, as well as state readers' choice lists in over twenty-eight states.