She is the only child of actress Annette Ekblom and actor Alun Lewis. When her parents divorced Amelia Warner was four years old and moved to London with her mother. She attended the Royal Masonic School for Girls and then at the age of 16 years, the College of Fine Arts in London. She studied art history at Goldsmiths College in London.
From July to November 2001, she was married to actor Colin Farrell. Since April 2013 she is married to Irish actor Jamie Dornan. End of November 2013 came their first child together, a girl, into the world.
She appeared in a 2000 BBC adaptation of Lorna Doone and had several minor roles in movies (eg Æon Flux ).