Back in February 2008, Nate Ruess split with The Format and formed a new band with the Format's touring partners. Nate asked Jack Antonoff of Steel Train and Andrew Dost of Anathallo to join him in a new project which was kicked off within a week in New York. "We stayed for a couple of months and just wrote, recorded and hung out," Andrew said in an interview.

They recorded their first demo and titled it "Benson Hedges". With materials in hand, the band approached Steven McDonald who produced for The Format. McDonald agreed to produce their first album and even played guitar in it. "At Least I'm Not as Sad (As I Used to Be)" was set as the first single and posted for free on the band's MySpace page.

Meanwhile, the band began searching for the right moniker. They did extensive search of a band called "Fun" over the internet and could not find any. But a few months into setting the name, they got an email from another act who claimed they have used "Fun" first. Therefore, Nate's band decided to add the period. "It was in our logo already because we like periods and That Dog. is one of my favorite bands and I think they always use a period," Andrew explained.

The first album was recorded in Los Angeles and released in April 2009 under the title "Aim and Ignite". It received positive reviews from music magazines and even peaked on Billboard Hot 200 chart at number 71. The threesome supported the album with extensive tours up to 2010, supporting Taking Back Sunday first before going for a headlining tour. They also continued to build fan base as the supporting acts of other bands such as Jack's Mannequin and Paramore.

Fun. signed a recording deal with Fueled by Ramen in August 2010 and the work for their second album started from there. They released a collaboration with label mate Panic At the Disco titled "C'mon" in May 2011. Their own first single came out four months later called "We Are Young", featuring Janelle Monae.

To the band's delight, the single managed to bring a lot of attention to the band. Beside sitting atop the Billboard Hot 100 chart, "We Are Young" was vastly used on TV shows such as "Glee" and "Chuck". "We Are Young" made Fun. the first multi-member Rock Band to make a Billboard debut with the number 1 spot on the Hot 100 since Nickelback's "How You Remind Me" in December 2001.

"Some Nights " was released as the band's second album in February 2012, fueled by another single "One Foot" and the title track. The album debuted at number 3 on the Billboard 200 with first-week sales of 70,000 copies in the United States.