Who sings the original tonight we are young song?

The original song "Tonight We Are Young" is performed by the American pop-rock band Fun. The song was released in September 2011 as the third single from their second studio album "Some Nights." Fun, which consisted of Nate Ruess, Andrew Dost, and Jack Antonoff, rose to prominence with "Tonight We Are Young," which became a global hit and topped various music charts internationally.