Christiansen began his career by racing in biathlon and cross-country skiing as a junior on the national level. In his youth, his greatest idol was Ole Einar Bjørndalen. Christiansen learned much about how to train from literature of and about Bjørndalen, and was inspired by Bjørndalen's training mentality, and started training a lot and hard, from a very early age. On the last day of the 2004 World Championships, Christiansen set a long-term goal of qualifying for the 2014 Winter Olympics. In 2008, Christiansen entered the Norwegian College of Elite Sport in Geilo.