She is best known for her portrayal of Dayna Mellanby in the third and fourth seasons of the television sci-fi series Blake's 7. Her recent television work includes roles in Lewis, Casualty, Skins, Midsomer Murders, The Last Detective and the Poirot episode "The Mystery of the Blue Train". Simon's film appearances include Cry Freedom and Milk and Honey, for which she was nominated for a Best Actress award. In 1992 she starred alongside Brenda Fricker in the TV film Seekers, produced by Sarah Lawson. She was also nominated for a Best Actress award for her performance in Golden Girls at the RSC.