Down was born in Langley, British Columbia. 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.
Down's most famous appearance is most likely in the TV series Mysterious Ways, where she played the role of Miranda, a physics graduate student who, together with Professor Declan Dunn (often the enthusiast behind the investigations) and psychiatrist Dr. Peggy Fowler (the other skeptic besides Miranda), tries to solve a range of mysterious or paranormal events. One of her high-profile roles was that of Jean Barolay in the re-imagined Battlestar Galactica series.