Myles was born in London. Her father, Peter Myles, is a vicar in Isleworth, West London and her mother, Jane, works in educational publishing; her paternal grandmother was Russian. Myles began her acting career after being spotted in a school play. Beforehand, she had been planning to accept a conditional place to study philosophy at Cambridge.
Since 1996, Myles has appeared in a number of both American and English films and television productions. She had a supporting role in the 2003 film, Underworld, and (in a brief flashback scene) its sequel, Underworld: Evolution. In 2006, Myles co-starred with actor James Franco in the romantic drama Tristan and Isolde, playing the role of Isolde.
Myles appeared as Madame de Pompadour in a 2006 episode of Doctor Who, The Girl in the Fireplace. She also co-starred opposite English actor Max Minghella, playing his love interest, in the quirky comedy Art School Confidential, which opened in May of 2006.
She has recently finished filming a BBC TV adaptation of Dracula in which she will play Lucy alongside Marc Warren, David Suchet and Dan Stevens.
Currently, she is filming Outlander (2007) with James Caviezel and Jack Huston.
Myles lives in Green Park and enjoys horse riding, skiing, skating and swimming. As of 2006, she is dating Scottish actor David Tennant, opposite whom she appeared in her guest role on Doctor Who. She was previously in a relationship with actor Charles Dance, whom she met while working on Nicholas Nickleby.
