She showed an interest for acting early, and during her younger years she used to write and produce her own plays.
After she graduated from H. D. Stafford Secondary School, Down studied at the American Academy of Dramatic Arts in California, and then the British American Dramatic Academy in Oxford.
She is married to actor David Richmond-Peck, whom she met while working on the series Robson Arms.
[1] Down's best known role is most likely Miranda, a physics graduate student who tries to solve a range of mysterious or paranormal events together with Professor Declan Dunn (often the enthusiast behind the investigations) and psychiatrist Dr. Peggy Fowler (the other skeptic besides Miranda), in the TV series Mysterious Ways.
Another high-profile role was that of Jean Barolay in the re-imagined Battlestar Galactica series.