Originally the lead singer of a band called The Format, Ruess, who is from Iowa City, Iowa, formed Fun with guitarist Jack Antonoff and keyboardist Andrew Dost. They released their first album, Aim and Ignite, in 2009, but their follow-up, 2012's Some Nights, proved to be their breakthrough album. It features the hit single "We Are Young", which features funk singer Janelle Monae. "We Are Young" won Fun a Grammy for Song of the Year. The title track also became a hit.
Ruess is currently working on a solo album, which is expected to be released sometime in 2015.
In addition to his work with Fun, Ruess also worked with pop-rock singer Pink on the song "Just Give Me a Reason", which earned them a Grammy nomination. He also contributed vocals to the Eminem song "Headlights".
Like Coldplay lead singer Chris Martin and country-pop singer Taylor Swift before him, Ruess was a guest advisor to all four coaches during the Knockout Rounds. He received praise from critics for his work on the show.