Harker has acted in both contemporary and classic works, on stage, in movies and in TV series. In 1990–91 she appeared alongside Clive Owen in "Chancer", and as the journalist Mattie Storin in the original "House of Cards". She later played Dinah Morris in the 1991 adaptation of "Adam Bede". She starred as Jane Bennet in the 1995 TV adaptation of Jane Austen's "Pride and Prejudice." She is featured as Emma Fitzgerald, the love interest of Superintendent Tyburn (Trevor Eve) in the BBC TV series, "Heat of the Sun" (1998). She appeared in the play, "On the Shore of the Wide World".