Margaret Grace Denig, better known as Maggie Grace, was born in Worthington, Ohio, a suburb of Columbus, the daughter of Linn and Rick Denig. She took to acting at an early age, performing in several local theatre productions, among them Jewish Community Center's Gallery Players' 2000 production of The Crucible. The director of that play, John S. Kuhn, said of Grace "Even at that young age she brought a lot to her work."

At 16, Grace left Ohio with her mother and headed for Los Angeles. The actress frequently found herself struggling to pay her rent. In 2001 she landed the eponymous role in the Sony Pictures web-serial Rachel's Room, which took the form of a teenager's video journal.

Over the following years, under her stage name Maggie Grace, she had guest appearances on several television shows, including CSI: Miami, Law & Order: Special Victims Unit and Oliver Beene, and portrayed Martha Moxley in the television movie Murder In Greenwich. In 2003, she played the Goth-influenced, estranged daughter of Tom Selleckand Wendy Crewson in the drama 12 Mile Road.

It was in 2004 that Grace landed her big break when she won the role of the affluent, lazy and self-centered Shannon Rutherford on J. J. Abrams' television pilot Lost. When Lost was picked up for a full season by AbcGrace relocated to Oahu, Hawaii where the show is filmed.

During the hiatus between the first and second seasons of Lost, Grace starred in the remake of the John Carpenter horror film, The Fog, alongside Tom Wellingand Selma Blair The film was nearly universally-panned upon its release that fall. She returned to Oahu for Lost's second season, where she filmed the first six episodes, before moving back to Los Angeles.

Maggie was widely rumored to have won the role of Shadowcat in X-Men: The Last Stand, but the role eventually went to Ellen Page Maggie later revealed that she had never been contacted about the role and was surprised to read she was up for the part in question. Grace was ranked #27 on Maxim's Hot 100 list of 2005.

After a break in 2006, Grace returned to both small and big screens in 2007. She returned to Oahu and Lost to film a guest spot in a season three episode, and she co-starred in two movies: Suburban Girl, alongside Sarah Michelle Gellarand Alec Baldwin and The Jane Austen Book Club.