Danish breakthrough

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]} At 17, he did not want the life of a professional footballer, and chose to play amateur football in Serie 3, the fourth lowest level of Danish football. For fun, he tried playing the position of goalkeeper, in which position he caught the attention of higher ranking clubs. Roskilde B 1906 offered him a contract in 1997, and he was Roskilde's goalkeeper for one season, before he followed his coach to Ølstykke.^{[citation needed]}

In 1998, he moved to OB in the second tier of Danish football, the Danish 1st Division.^{[citation needed]} He helped OB win promotion to the top-flight Danish Superliga, where he got his national breakthrough. When OB legend Lars Høgh retired in January 2000, a string of strong displays by Christiansen showed a strong temper and good reflexes.^{[citation needed]} He looked the long term replacement of Lars Høgh, though Christiansen never got the chance to make a decent bid for Høgh's record 817 games for OB. 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.^{[citation needed]}

On the bench in Glasgow

In Glasgow, he played alongside fellow Dane Peter Løvenkrands, with whom he became good friends,^[1] and he played a handful of games in his first time at Rangers, including a few outings in the UEFA Champions League. His league debut was a 3–0 home defeat to Kilmarnock.^[2] When first choice goalkeeper Stefan Klos returned from his injury, he once again took control of the goalkeeper spot. Christiansen could not force his way into the starting line-up, and he was put on loan.

His first loan deal with Danish Superliga club Vejle in 2001 was a personal success for Christiansen. Though Vejle was relegated to the 1st Division, he was called up to the Danish national team. After the period in Vejle, Christiansen was loaned out to VfL Wolfsburg.^[3] This period was one of the worst in his career, the result being that he was dropped from the national team. He did not play a single first team game for Wolfsburg, and did not make many friends in Germany. Christiansen later said he would rather warm the bench at Rangers, than in Wolfsburg.^[1]

Danish success

In the winter transfer window of the 2003–04 Superliga season, Christiansen returned to Denmark once more to play for Viborg, following a string of goalkeeper switches; former Viborg goalkeeper Arek Onyszko moving to Odense, replacing Karim Zaza, who had transferred to Brøndby. At Viborg, Christiansen showed the impressive form that he had displayed for Odense and Vejle once more.

Following one and a half year at Viborg, Christiansen moved to Copenhagen (FCK) in the summer of 2005. At FCK, he was assigned the no. 1 jersey as the club's first choice for the goalkeeping position. His debut in the FCK-jersey came on 20 July 2005, keeping a clean sheet as AaB were defeated 1–0 at Aalborg Stadion in Aalborg. In the autumn 2006, he was an important part of FCK's participation in the 2006–07 UEFA Champions League, producing many great saves. This brought renewed interest from foreign clubs, as he and teammate Michael Silberbauer were both rumoured on their way to English club Everton in the 2006 winter transfer window.^[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.^[6]

In the opening match of the 2007–08 season, against Nordsjælland at Farum Park, Christiansen was close to score on a header, as it hit the inside of the post, and was parried by Nordsjælland keeper Kim Christensen, after a corner kick deep into extra time.^[7] In May 2008 he was linked with a £1 million move to West Bromwich Albion. For the 2009–10 season, FCK bought Johan Wiland as a backup. When Christiansen was injured against Brøndby IF in the seventh Superliga game of the season, Wiland replaced him with such success that Christiansen was permanently demoted to the bench.^[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.^[8]

He signed for Elfsborg of the Allsvenskan championship in June 2010.^[10]