Robertson began acting when she was 10, launching a television and film career in Canada. During this time, she attended the prestigious Hamilton high school Hillfield Strathallan College. Her first continuing series was in the Canadian television program Maniac Mansion, from 1990-1993. She played Tina Edison, the eldest of three children and daughter to Dr. Fred Edison (Joe Flaherty). She did not debut on the big screen until her small role in the Brenton Spencer film Blown Away. She was cast as Clare Arnold in Beverly Hills, 90210, where she remained until 1997. Her ex-boyfriend, director Gregg Araki, cast her in the lead of two of his films, Nowhere (1997) and Splendor (1999).