Born in Roskilde, Christiansen competed with later national team player Peter Madsen to be the best forward on Zealand in his teenage years.
[citation needed] He helped OB win promotion to the top-flight Danish Superliga, where he got his national breakthrough.
As Scottish club Rangers suffered injuries in their goalkeeping staff, the search for replacements turned to Christiansen, who was eager to move abroad at 22 years of age.
In the autumn 2006, he was an important part of FCK's participation in the 2006–07 UEFA Champions League, producing many great saves.
[4] The transfer never materialized, and in January 2007, Christiansen expressed his desire to further his career by moving to a club in a bigger league,[5] but a new five-year contract cancelled every rumour.
[8] Media reports suggested he wanted a transfer,[9] and when FCK bought Kim Christensen as a new backup keeper in the Summer 2010, Christiansen was expected to leave the club.
He was chosen for the Danish squad at the 2002 FIFA World Cup in South Korea and Japan as a backup for starting national team goalkeeper Thomas Sørensen, and was an unused substitute throughout the tournament.
Before the 2010 FIFA World Cup, Christiansen lacked playing time at FCK, and found himself in contention with Kim Christensen for the spot as third goalkeeper in the squad for the finals.
Eventually Morten Olsen chose Christiansen for his team,[11] and he spent his time at the tournament as an unused substitute.
After Christiansen left Vendsyssel in the summer 2017, he was officially announced as the new assistant manager of Danish 1st Division club AB.
[14] On 15 July 2019, it was announced, that Christiansen had left Fremad Amager because he wanted to stay closer to his family and then became the new goalkeeper coach of Viborg.