Kelly Reilly is an English actress, who grew up in Chessington, Greater London, in a working-class family, where her father was a policeman and her mother worked at Kingston Hospital. She did not attend drama school due to financial constraints and an inability to articulate her interest in acting.

Reilly was inspired to act after seeing a performance of The Resistible Rise of Arturo Ui. At age 17, she made her professional debut in an episode of Prime Suspect, acting alongside Helen Mirren while still studying for her A-levels. She would later play the younger version of Mirren's character in the flashback sequences of the film Last Orders.

Her performance in 2004 in After Miss Julie at the Donmar Warehouse saw her nominated for an Olivier Award, as its youngest ever "best actress" nominee, a position she now shares with Anna Maxwell Martin. She won the Cannes Film Festival 2005 "Best Actress in an Independent Film" award for her performance in Mrs Henderson Presents (2005). In 2006 she picked up "best newcomer" awards from the London Critics Circle and the Empire Film Awards.

She is also well-known in France because of her role of Wendy, an English Erasmus student, in the film L'Auberge espagnole by Cédric Klapisch, in which she starred opposite Romain Duris, Audrey Tautou, Judith Godrèche and Cécile de France. Wendy became the romantic lead in the 2005 sequel Les Poupées russes and Reilly was nominated for a César award for best supporting actress in 2006.

Reilly appears in the forthcoming film Eden Lake and in early 2008, she appeared in ITV1's adaptation of Jake Arnott's crime novel He Kills Coppers. She appeared in Othello at the Donmar Warehouse from 30 November 2007 to 23 February 2008, alongside Chiwetel Ejiofor and Ewan McGregor.