Nissen started the North American continental championship Nor-Am Cup in February 1995 - but initially in the ski ballet discipline , which was still being held at that time , and occasionally in the mogul slope disciplines. In 1998 he finally turned to freestyle ski jumping. He made his debut in the Freestyle World Cup on December 4, 1999 in Whistler-Blackcomb , where he finished twelfth and won his first World Cup points. On January 23, 2000 he surprised with his first World Cup victory in Heavenly . Nissen struggled to confirm this success. He started the 2001/02 season with a 2nd place in Mount Buller ; due to the strong competition within the team, this was not enough to qualify for the 2002 Winter Olympics.
For the next two seasons, Nissen's results were inconsistent (between ranks 2 and 31). In 2005 he finished second and third in the World Cup, and with 5th place in Ruka he achieved his best result at a world championship. In the 2005/06 World Cup season he stood on the podium four times; Among other things, he achieved his second (and last) World Cup victory on January 8, 2006 in Mont Gabriel . In the discipline ranking he took second place behind the Belarusian Dzmitryj Daschtschynski . At the 2006 Winter Olympics , he jumped to 5th place.
Nissen's best result in 2007 was a 2nd place. Due to an injury, he was sidelined for the entire 2007/08 season. With another 2nd place, he returned to the top of the world at the beginning of 2009. Nissen took part in the 2010 Winter Olympics, where he finished fifth like four years earlier. Immediately after the Olympic competition, he withdrew from top-class sport.