Beginning acting in her hometown of Bedford, New York, she moved from the stage to her first film, Random Hearts (1999).
Her notable roles include appearances in the Academy Award-winning film Brokeback Mountain, playing the daughter of Heath Ledger's character, and on the Fox television series 24, as computer analyst Shari Rothenberg.
She has since appeared in the feature films We Are Marshall (2006), Shooter (2007), and Transsiberian (2008).
Mara joined the cast of the HBO series Entourage for the sixth season, and co-stars in The Open Road (2009) with Justin Timberlake. She will play Bethany Cabe in Iron Man 2 (2010).
Mara was born and raised in Bedford, New York, the daughter of Chris Mara, a scout for the New York Giants, and Kathleen (née Rooney).
She is Irish-Italian-American, her family name used to be O'Mara. She has one older brother, Daniel, and two younger siblings, Patricia and Conor.
Mara wanted to be an actress since seeing Les Misérables at a young age; she said she "fell in love with Broadway and musicals", and grew up watching movie musicals on television and going to Broadway shows with her mother.
She was especially a fan of Judy Garland's films. Mara began acting at the age of nine in a school musical, and attended several youth theater-arts schools, and appeared in community theater and in school plays.
Mara described herself to Esquire magazine as "painfully shy" while growing up, and said she only had one friend.
Beginning at a young age, Mara continually asked her mother to help her get an agent. Mara's mother got the name and address of a management company, sent in a photograph, and Mara signed with her first agent, beginning her professional career at the age of 14. Mara's first audition was for the television drama Homicide: Life on the Street.
