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.

Apart from his musical career, Wentz has been involved in various entrepreneurial ventures. Fall Out Boy bandmate Patrick Stump says of Wentz's endeavors: "It scares me sometimes, watching him. The two seconds you're not with that dude he's made 30 decisions that are going to affect our band for the rest of the year." Wentz's company, Clandestine Industries, distributes books, clothing, and other merchandise. On August 2, 2007, fashion company DKNY joined a partnership with Clandestine Industries. Wentz himself has served as a model on the DKNY/Clandestine promo website. In April 2007, Pete came out with his own signature Squier Precision Bass. It has a black body with a red shell pickguard and special graphics that include Wentz's own red bat/heart design on the body, plus a black bat/diamond fingerboard inlay at the 12th fret. It also features Wentz's signature on the back of the headstock. Wentz owns a very similar custom Fender bass with a purple pickguard and bat/heart. In 2008, Fender gave his son, Bronx Wentz, a three-quarter-sized modified version of his guitar. Wentz opened a nightclub in New York with his bandmates as well as members of Gym Class Heroes, The Academy Is..., and Cobra Starship; the bands' managers are also involved in the enterprise. Called Angels & Kings, the club occupies the former space on 11th Street near Avenue A that housed the Orchid Lounge. Notable guests, including Tommy Hilfiger, arrived for the grand opening on April 20, 2007. In June 2007, Wentz celebrated the opening of Angels & Kings' second location in Chicago. On December 13, 2008, Wentz, along with Travis McCoy of Gym Class Heroes, created several pieces for an art exhibit at Gallery 1988 in Los Angeles called "Without You, I'm Just Me." The exhibit closed on December 24, 2008. Wentz appeared in the season 5 episode of CSI: NY, "Point of No Return", along with then-wife Ashlee Simpson. Wentz also hosted the Australia MTV VMAs on March 27, 2009. Wentz collaborated with Mark Hoppus on the track "In Transit" on the Almost Alice soundtrack for the 2010 movie, Alice in Wonderland. He was also a judge for the 10th and 11th annual Independent Music Awards to support independent artists' careers.

Did Pete work on any TV projects?
Wentz also hosted the Australia MTV VMAs