He is one of only seven contestants in the Norwegian Idol history who succeeded in staying out of the "bottom three/two" places in weekly votes.

He subsequently won the title for the World Idol on 1 January 2004, singing the hit "Beautiful Day" by U2, beating competitors from ten other nations, including the more famous Idol winners, Britain's Will Young, and favourite Kelly Clarkson of the United States, and scoring the first place in 10 out of 11 countries eligible to vote for him (Norwegian voters being unable to vote for him).

In the show presenting the entries on 25 December, Ian Dickson, the Australian (English ex-pat) judge, said: "Kurt, you are a hell of a marketing challenge, because you have the voice of an angel, but you look like a Hobbit.

Nilsen performed the duet, "It's All Coming Back to Me Now", alongside Norwegian Pop/Alternative Rocker, Marion Raven at the One Call Event.

Taking the place of Meat Loaf, with whom Raven recorded the track for the album Bat Out of Hell III In 2006, he and three other Norwegian artists Askil Holm, Espen Lind, and Alejandro Fuentes, all in the same management, joined forces and went on tour in March as what was known by the media as "The New Guitar Buddies".

Nilsen performed the duet "When You're Gone" alongside English pop singer, and former-Spice Girls member, Melanie C at the Top 20 event at Rådhusplassen in Oslo, Norway in the summer of 2007.

In late February 2010, Kurt and Elin sang the duet "The Water is Wide" on the TV2 show Senkveld, to great acclaim.