She was born in Thurles, County Tipperary, Ireland. Her roles include Victoria in Unleashed (2005), and Kate Kelly in the 2003 film Ned Kelly. She also appeared in Intermission (2003) and as Octavia of the Julii in the HBO/BBC series Rome and as Masha in The Last Station (2009)
In 2001, she originated the role of Mairead in the The Lieutenant of Inishmore by Martin McDonagh which she performed at The Royal Shakespeare Company and The Atlantic Theatre Company, New York. For this production she recorded the song The Patriot Game with The Pogues. In the same year, at the age of 19, she played the role of Ophelia in Hamlet, making her the youngest actress to ever play that role for the RSC. In 2009, she appeared in another play by Martin McDonagh The Cripple of Inishmaan for which she won a Lucille Lortel award and a Drama Desk award.