Adam Charles Clayton, the oldest child of Brian and Jo Clayton, was born on 13 March 1960 in Chinnor, Oxfordshire, England. His father was a pilot with the Royal Air Force, who moved into civil aviation, and his mother was a former airline stewardess. When he was 4 years old, Clayton's father worked in Kenya as a pilot with East African Airways, the family being resident in Nairobi (Clayton regards this as the happiest period of his childhood). In 1965, the family moved to Malahide, County Dublin in the Republic of Ireland, where Clayton's brother Sebastian was born.

In September 1976, Mullen put an advert onto the school's bulletin board seeking other musicians to form a band; Clayton showed up for the first meeting and practice, so did the Edge with his older brother Richard Evans ("Dik"), Bono, and Ivan McCormick and Peter Martin who were two of Mullen's friends. McCormick and Martin left the band soon after its inception.  While the band was a five-piece (consisting of Bono, the Edge, Mullen, Dik Evans, and Clayton) it was known as "Feedback". The name was subsequently changed to "The Hype", but changed to "U2" soon after Dik Evans left. Clayton stood in as the nearest thing that the band had to a manager in its early life, handing over the duties to Paul McGuinness in May 1978. 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.  In 1995, after the 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 1997's Popmart tour Clayton has not sung live in any capacity for the band. In 1996, while still in New York, Clayton collaborated with Mullen to re-record the Mission: Impossible theme.

was he married?