He is most famous for playing the gay character "Gabriel" in the movie Trick. He has also acted in numerous other television series and films. In 2001, Christian teamed up with Trick co-star John Paul Pitoc in the feature-film Thank You, Good Night co-starring with Mark Hamill and Sally Kirkland. Campbell played the recast Bobby Warner on All My Children, replacing Brian Gaskill for the role after a seven-year absence from 2004 to 2005. Before its abrupt cancellation, he had a starring role in the NBC drama The Book of Daniel. He has also Starred in Shawn Ku's "Pretty Dead Girl".
On stage his work includes the Jonathan Larson musical Tick, Tick... BOOM!, which he has played on a National Tour of America and in London at the Menier Chocolate Factory (July – September 2005). He has also portrayed the lead character of "Jimmy Harper" in all stage productions of Reefer Madness: The Musical as well as the Showtime network adaptation, Reefer Madness: The Movie Musical.
His siblings are actress Neve Campbell, Damian Campbell, and actor Alex Campbell.