She is known for playing Shannon Rutherford on the ABC television series Lost (2004–2006; 2010), Kim Mills in the Taken trilogy (2008–2014), Irina in The Twilight Saga (2011–2012), and Althea Szewczyk-Przygocki in Fear the Walking Dead (2018–2021).

[5][6] As a child, Grace was a voracious reader and a self-described "Shakespeare nerd"[7] telling the Los Angeles Times that at age 13, she "was really into Jane Austen, kind of like how some kids are into Star Trek".

[6] She landed her first role in Rachel's Room, a 2001 web-based video series about the affairs inside a teenage girl's bedroom that was created by Dawson's Creek executive producer Paul Stupin.

[9] She went on to feature in minor roles on the television series CSI: Miami, The Lyon's Den, Miracles, Like Family, Cold Case and Law & Order: Special Victims Unit, and the films Twelve Mile Road and Creature Unknown.

Executive producer Carlton Cuse said that Grace's departure from the show was "sort of a win-win" as she was eager to enter a full-time career in film.

[19] Grace's next role was in the 2007 independent film Suburban Girl, alongside Sarah Michelle Gellar and Alec Baldwin.

[21] After the filming of The Jane Austen Book Club was completed, Grace briefly returned to Hawaii to shoot a guest spot on the Lost season 3 episode "Exposé".

[21] She starred in the 2008 thriller film Taken with Liam Neeson, who was at the top of a list of male actors Grace wished to work with that she had written just two months before she was cast.

[23] In 2010, Grace starred in the drama Flying Lessons,[24] and appeared opposite Tom Cruise and Cameron Diaz in James Mangold's film Knight and Day,[25] as well as in Faster, with Dwayne Johnson.

[31] While still working on Lost, Grace and Ian Somerhalder adopted a feral cat named Roo which they found "literally dying" in the jungle on the set.

"[37] She is a self-proclaimed Anglophile, having written to a pen pal in the Lake District from the age of eight, and admiring a number of English poets, including William Shakespeare; she first visited England when she was thirteen.