Hamilton is best known for her roles in costume drama. She appears as Ruby Pratt, one of the major characters in the BBC1 series Lark Rise To Candleford. Other roles have included Mrs Forster in the Emmy award-winning British 1995 series Pride and Prejudice and Maria Bertram in a 1999 film of Mansfield Park. She also played Queen Victoria in the BBC-TV production Victoria & Albert in 2001.
She also appeared in Midsomer Murders, Series 4 Episode 1, "Garden of Death" as Hilary Inkpen-Thomas, a downtrodden illegitimate daughter who becomes a killer.
She has been a member of the Peter Hall Company, the Royal Shakespeare Company and the National Theatre, as well as appearing in the West End and on Broadway. In 1995, she appeared in Ibsen's The Master Builder directed by Peter Hall and starring Alan Bates and Gemma Jones.
She is married to fellow actor Mark Bazeley, and they have a son.