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 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.
Most recently, Myles appeared as Madame de Pompadour in a 2006 episode of Doctor Who, The Girl in the Fireplace, and co-starred opposite English actor Max Minghella, playing his love interest, in the quirky comedy Art School Confidential, which opened in May of 2006.
