Wentz was born Peter Lewis Kingston Wentz III, in Wilmette, Illinois, an affluent suburb of Chicago. He is the son of Dale (nee Lewis), a high school admissions counselor, and Pete Wentz II, an attorney. He is of English and German descent on his father's side and Afro-Jamaican on his mother's side. He has a younger sister, Hillary, and a younger brother, Andrew.

In 2002, Fall Out Boy released an EP called Fall Out Boy/Project Rocket Split EP. Soon after, in 2003, the band released their mini-LP Fall Out Boy's Evening Out with Your Girlfriend on Uprising Records. This album would later be digitally remastered and reissued after the band's third, successful full-album release From Under the Cork Tree, on the major label Island Records. In 2003, the band released their first full-length album, Take This to Your Grave through Fueled By Ramen. Fall Out Boy signed with major label Island Records in 2003 and in 2004 released an acoustic EP and DVD entitled, My Heart Will Always Be the B-Side to My Tongue.  Their third album, From Under the Cork Tree, was released in 2005. Wentz wrote the lyrics to the lead single, "Sugar, We're Goin Down" with his dad in Chicago; the song peaked at #8 on the Billboard Hot 100 and spent months in the top 50 of the Hot 100, marking five weeks in the top 10 and fourteen weeks in the top 20. The band's major label debut album has since been certified double platinum by the RIAA as well as "Sugar, We're Goin Down."  In 2007, Fall Out Boy's fourth album, Infinity on High was released to major success, debuting at #1 on the Billboard 200 with 260,000 sales, spurred by the #2 charting lead single, "This Ain't a Scene, It's an Arms Race". The second single, "Thnks fr th Mmrs" sold more than 2 million units in the US. The band's fifth studio album, Folie a Deux was released on December 13, 2008, and debuted at #8 on the Billboard 200. The band toured extensively in support of their albums.  On November 20, 2009, the four band members announced they will be taking an indefinite hiatus, saying they were unsure of the future of the band. Wentz has said that his personal reason for taking a break is that he feels that his name and marriage to pop singer Ashlee Simpson had become a hindrance for the band. He added: "I think the world needs a little less Pete Wentz".  On February 4, 2013, the band announced their hiatus was over, via their official webpage. They released a new single off their upcoming album, a video for the single, upcoming tour dates and a pre-order campaign for the new album titled Save Rock and Roll.

What album did they release?
In 2002, Fall Out Boy released an EP called Fall Out Boy/Project Rocket Split EP.