Christensen was selected with 40th overall pick by the
Geelong Football Club in the
2009 AFL draft. Prior to the draft, however, he was predicted to be drafted in the range of 10–25, and was interviewed by a total of 12 clubs in the recruiting process. Christensen did not make a senior appearance in his first season with Geelong; instead, he played with the club's
VFL reserves team, where he played in 16 games. His consistent performance in the VFL was recognised in being listed among the "best players" for nine of these matches,
Geelong (2011–2014) Christensen made his debut in the second round of the
2011 AFL season against
Fremantle at
Subiaco Oval in Perth. As the club's substitute for the match, he subbed in late in the third quarter and finished the game with eight disposals, assisting Geelong to an 11-point victory. As a result of his performance in Geelong's round 18 game against
Richmond, in which he garnered 26 disposals and scored two goals, Christensen was nominated for the
2011 AFL Rising Star award. In 2020 he was named in the
St Joseph’s College team of champions, recognising the best
VFL/AFL players to have attended the school. He retired on 21 October 2020. ==Post-AFL career==