Fall Out Boy were formed in Wilmette (a suburb of Chicago) early 2001 by friends Joe Trohman (lead guitar) and Pete Wentz (bassist), who had both played in various bands in the Chicago area. Trohman introduced himself to Patrick Stump in a Borders bookstore when he overheard him talking about the band Neurosis, in which they shared a mutual interest. Stump originally auditioned as a drummer, but as soon as his vocal range was discovered, he became the lead singer. The band was complete when 2 other Chicago musicians were recruited - T.J. Raccine on guitar, and a drummer simply credited as Mike. In early 2002, the band self released a demo, and followed it up with an EP called “Split” in May. Nameless for their first 2 shows, at the end of the second show the band asked the audience to yell out ideas for a name, with one suggesting "Fallout Boy", in reference to the sidekick of the Simpsons cartoon character “Radioactive Man”.
Fall Out Boy released a mini LP, “Fall Out Boy's Evening Out with Your Girlfriend”, on Uprising Records, in 2003, but after it’s release, line up changes were rife, with Andy Hurley (formerly of Racetraitor) joining on drums, and Raccine and ‘Mike’ leaving, causing Stump to pick up the rhythm guitar in addition to his lead vocal duties. After signing to Fueled by Ramen, they released their first full length album, “Take This to Your Grave” in May 2003, recorded at the the Butch Vig owned Smart Studios in Madison, Wisconsin, which sold well and eventually achieved Gold status (after their later albums had been released). The acoustic EP “My Heart Will Always Be the B-Side to My Tongue” was released on Fueled by Ramen in May 2004, which debuted at number 153 on the Billboard 200.

In May 2005, Fall Out Boy released their major label debut, “From Under the Cork Tree”, debuting at number 9 on the Billboard 200, and selling over 68,000 copies in its first week. First single "Sugar, We're Goin Down" peaked at number 8 on the Billboard Hot 100, number 6 on the Pop 100, and number 3 on the Modern Rock Charts. Second single "Dance, Dance" emulated its success and became their second Top 10 Single, peaking at number 9 on the Hot 100, reaching number 6 on the Pop 100, and number 2 on the Modern Rock Charts. Third single "A Little Less Sixteen Candles, a Little More 'Touch Me'" was less successful, but still managed to peak at number 65 on the Hot 100. “From Under the Cork Tree” achieved double platinum status and has sold over 2.5 million copies in the US alone. It also helped the band get nominated for "Best New Artist" at the 2006 Grammy Awards.

In February 2007, “Infinity on High” was brought out, and reached number 1 on the Billboard 200, selling 260,000 copies. Lead single "This Ain't a Scene, It's an Arms Race" peaked at number 2 on both the UK Singles Chart and the Billboard Hot 100, and number 1 on the Pop 100. Second single "The Carpal Tunnel of Love" reached number 81 on the Hot 100 on digital sales alone, and "Thnks fr th Mmrs" climbed to peaked 11 on the Billboard Hot 100 and number 12 on the UK Singles Chart.

Fall Out Boy have collaborated with rappers Kanye West (who produced and featured on a remix of "This Ain't a Scene, It's an Arms Race") and Timbaland (where Stump and Wentz contributed written material for his album “Shock Value”), and Stump has featured on 2 songs with Gym Class Heroes (also signed with Fueled by Ramen), including the band's hit single "Cupid's Chokehold". Fall Out Boy have also covered Michael Jackson's “Beat It” with John Mayer as a guest guitarist – released in March 2008 it debuted at number 22 on the Billboard Hot 100, eventually reaching 19.