Myles is a native of Ystradgynlais, Wales. Her television roles have included appearances in EastEnders, and the television film Score. In 2002 and 2003, Myles was nominated for Best Actress in the BAFTA Cymru Awards for her role as Ceri on the BBC Wales drama Belonging. Myles played Lavinia in the 2003 Royal Shakespeare Company production of Titus Andronicus. In 2005, she appeared opposite Michael Gambon in Henry IV, Part I and Henry IV, Part II at the Royal National Theatre. In 2005, The Western Mail ranked Myles seventh in its annual list of the 50 sexiest women in Wales.