The record deal, which includes both the brothers' Youtube phenomenon The Fox and future songs, was reported by The Hollywood Reporter on Saturday.
"It's a fantastic signing," Guttorm Raa, the head of Warner Music in Norway, told VG newspaper. "This means that they have a major global network working to promote their song, as well as other releases for Warner. It is huge."
Raa later explained that the deal had been signed even before the song was released, and was not a new deal, as had been reported in the US.
In an interview with The Hollywood Reporter, the brothers, who perform under the name Ylvis, said that their comedy and talk show career would always come first.
“We're comedians…and we like to sing,” Bård Ylvisåker said.
"We'll never pursue pure music as a career," his brother Vegard added. “This is very new for us and everyone is asking, ‘What are you going to do now?’ We don’t know. We’re busy trying to figure out what to do the next day.”
On Friday afternoon, the brothers appeared on the Ellen DeGeneres show, performing The Fox alongside their host (see videos below).
On Saturday morning, they moved to Las Vegas where they performed in front of a 20,000 strong audience at the iHeartRadio music festival.
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The Fox has now reached the Top 20 on the US iTunes chart, and holds the 25th place on the Billboard Hot 100.
The Youtube video has been viewed 47 million times in the two weeks since it was released.