Christensen's first acting role was on the television series Family Passions, which aired on Canadian television in September of 1993, at the age of twelve. The following year he acquired a minor role in John Carpenter's In the Mouth of Madness. From 1995 through 1999, he appeared in several movies and television shows, including Harrison Bergeron, Forever Knight, Goosebumps, The Virgin Suicides, and Are You Afraid of the Dark?.

He acquired wider notice while starring in Fox's Family Network TV series, Higher Ground in 2000, portraying a teen who was sexually molested by his stepmother, who then turned to drugs in his despair.