Margaret Grace was born in Worthington, Ohio. She dropped out of high school to move to Los Angeles with her mother after her parents' divorce. While struggling financially, she landed her first role as the title character in the web-based video series Rachel's Room in 2001. She went on to earn a Young Artist Award nomination in 2002 with her portrayal of 15-year-old murder victim Martha Moxley in the television movie Murder in Greenwich.
In 2004, she was cast as Shannon Rutherford in the television series Lost, on which she was a main cast member for the first two seasons, winning a Screen Actors Guild Award shared with the ensemble cast. After leaving the series, she was keen to work more prominently in films.
- The Fog
- The Jane Austen Book Club
- Knight & Day
- About Alex
- We'll Always Have Paris
- Decoding Annie Parker
- Twilight: Breaking Dawn
- She was named one of Variety's Top 10 Actors to Watch.
- She still has the same car she bought when she was 18.