Starting his career in 1999 on Team EC-Bayer, Christensen would win his sole victory that year. He switched to Team Coast in 2000 where he rode with the big names of two-time Vuelta a España winner Alex Zülle and Tour de France stage winner Fernando Escartín. When the team turned into Team Bianchi in 2003, to solely focus on former Tour de France winner Jan Ullrich's 2003 Tour de France campaign, Christensen didn't follow the bulk of the Team Coast riders to Team Bianchi. Instead, he went on to ride for Team CSC where Christensen rode in support of team captain Tyler Hamilton in the 2003 Tour de France. Christensen ended his career at the end of the 2004 season.