Adam Charles Clayton is the bassist of the rock band U2. Clayton has resided in County Dublin since the time his family moved to Malahide when he was five years old in 1965. Clayton is well-known for his bass playing on songs such as "New Year's Day" and "With or Without You". He has worked on several solo projects throughout his career, such as his work with fellow band member Larry Mullen Jr. on the theme of 1996's Mission: Impossible.

Clayton is the eldest child of Brian and Jo Clayton, born on 13 March 1960 in Chinnor, Oxfordshire, England. When Clayton was five years old, his family moved from Oxfordshire to Malahide, near Dublin, where Clayton's brother Sebastian was born. The Clayton family became friends with the Evans family, with their sons Dick and Dave (more commonly known as The Edge), who were both in the original group, Feedback, that spawned U2.

Clayton attended boarding school firstly at Castle Park School in Dalkey, then at St. Columba's in Rathfarnham. He later changed school to Mount Temple Comprehensive School in Dublin, where he met fellow bandmates Paul "Bono" Hewson and Larry Mullen Jr., and was reunited with his boyhood friend Dave "The Edge" Evans. In 1981, around the time of U2's second, spiritually charged album, October, a rift was created in the band between Clayton and McGuinness, and the three other band members. Bono, The Edge, and Mullen had joined a Christian group, and were questioning the compatibility of rock music with their spirituality. However, Clayton, with his more ambiguous religious views, was less concerned, and so was more of an outsider, until Bono's wedding to Alison Hewson (Neé Stewart), in which Clayton was the best man.

In August 1989, Clayton made newspapers around the world when he was arrested in Dublin carrying a small amount of marijuana. However, he avoided conviction by making a large donation to charity, and has later been regretful, saying "It was my own fault. And I'm sure I was out of my head - emotionally apart from anything else. But it is serious because it is illegal." Clayton has also had alcohol problems, which came to a head on 26 November 1993 when he was so hung over that he was unable to play that night's show in Sydney. After that incident, however, he gave up alcohol.

In 1995, after the groundbreaking Zoo TV Tour and Zooropa album, Clayton headed to New York with bandmate Mullen to receive formal training in the bass; until then Clayton had been entirely self-taught. During that period, he worked on U2's experimental album, released under the pseudonym "Passengers", entitled Original Soundtracks 1. That album features one of the few instances where Clayton has appeared as a vocalist; he spoke the last verse of "Your Blue Room", the album's second single. Prior to this Clayton had only provided live backing vocals to tracks such as "Out of Control", "I Will Follow", "Twilight" and "Bullet the Blue Sky". Since 1998's Popmart tour Clayton has not sung live in any capacity for the band.

Clayton remains the only bachelor member of U2. During the early 1990s, he was involved with and briefly engaged to British supermodel Naomi Campbell. He also had a long-standing relationship with Suzanne "Susie" Smith, a former assistant to Paul McGuinness; they were engaged in 2006, but the pair broke up in February 2007.

As a bass player, Adam Clayton is recognized for his unique playing style and rhythms that are apparent in many songs, most notably "New Year's Day", which evolved out of an attempt to play Visage's song "Fade to Grey", and "With or Without You". His style has been influenced by many different styles, such as Motown and reggae, and has evolved over his years in U2. He cites artists such as Paul Simonon of The Clash as influences on his musical style. When Clayton first joined the fledgling U2, he did not have any formal training in the bass. Consequently, his style developed without any formal training until 1995. In the early years of U2, his bass was generally a simple part in 4/4 time.] Bono said of Clayton's early bass playing, "Adam used to pretend he could play bass. He came round and started using words like action and fret and he had us baffled. He had the only amplifier so we never argued with him. We thought this guy must be a musician, he knows what he's talking about and then one day we discovered he wasn't playing the right notes, that's what's wrong ". However, as the group grew and evolved, his bass became more complicated, as is the case on 1987's The Joshua Tree and 1988's Rattle and Hum. Still, he continues to play simple basslines in many songs; for example, 2000's "Beautiful Day", with a simple 8th-note part.

Clayton has sung on several occasions, for example, on the song "Endless Deep", the B-side to the single "Two Hearts Beat As One" from 1983, he made an appearance singing. Clayton can be heard speaking on "Tomorrow ('96 Version)" (a rerecording of "Tomorrow" that he arranged) a song from U2's 1981 album October. He plays the guitar on a few occasions, most notably the song "40", where he and guitarist The Edge switch instruments. He also plays the introduction to "City of Blinding Lights" on the keyboard.

Clayton has worked on several side projects throughout his career. He played on Robbie Robertson's self-titled album from 1987, and has also performed with Maria McKee. He joined U2 producer Daniel Lanois and bandmate Larry Mullen Jr. on Lanois's 1989 album Acadie, playing the bass on the songs "Still Water" and "Jolie Louise". In 1994, Clayton played bass along with bandmate Larry Mullen Jr. on Nanci Griffith's album Flyer, playing on the songs "These Days in an Open Book", "Don't Forget About Me", "On Grafton Street" and "This Heart".