Clayton is the oldest child of Brian and Jo Clayton. His father is a pilot with the Royal Air Force, who moves into civil aviation, and his mother is a former airline flight attendant. When he is 4 years old his father works in Kenya as a pilot with East African Airways. Clayton regards this as the happiest period of his childhood. In 1965 the family moves to Malahide, County Dublin, where Clayton’s brother Sebastian is born. The Clayton family becomes friends with the Evans family, including their son, David, who later becomes a fellow U2 band-member with Clayton.
When he is eight years old Clayton is sent to the private junior boarding Castle Park School in Dalkey, Dublin, which he did not enjoy because he is not particularly sports orientated. At age 13 he enters the private St. Columba’s College secondary school in Rathfarnham, Dublin. Here he makes friends with other pupils who are enthusiastic about pop/rock music. It is here in the school band where Clayton plays the bass guitar for the first time.
Clayton later changes school to Mount Temple Comprehensive School in Dublin, where he meets future bandmates, Paul Hewson (aka “Bono“) and Larry Mullen Jr., and is reunited with his childhood friend David Evans (aka “The Edge”). In September 1976, Mullen puts an advert onto the school’s bulletin board seeking other musicians to form a band. The original band is a five-piece band known as “Feedback,” consisting of Bono, The Edge, Mullen, Dik Evans, and Clayton. The name is subsequently changed to “The Hype,” but changes to “U2” soon after Dik Evans leaves the band. Clayton stands in as the nearest thing that the band has 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 October album, a rift is created in the band between Clayton and McGuinness, and the three other band members. Bono, The Edge, and Mullen have joined a Christian group, and are questioning the compatibility of rock music with their spirituality. However, Clayton, with his more ambiguous religious views, is less concerned, and so is more of an outsider, until Bono’s wedding to Alison Hewson (née Stewart), in which Clayton is the best man.
Clayton makes international headlines in August 1989 when he is arrested in Dublin for carrying a small amount of marijuana. He avoids conviction by making a large donation to charity. Clayton also has alcohol problems, which come to a head on November 26, 1993, when he is so hung over that he is unable to play that night’s show in Sydney, the dress rehearsal for their Zoo TV concert film. Bass duties are fulfilled by Clayton’s technician Stuart Morgan. After that incident, however, Clayton gives up alcohol.
In 1995, after the Zoo TV Tour and Zooropa album, Clayton heads to New York City with bandmate Mullen to receive formal training in the bass as until then Clayton has been entirely self-taught. Bono says 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, y’know?”
In 2011 Clayton becomes an ambassador for the Dublin-based St. Patrick’s Hospital‘s Mental Health Service “Walk in My Shoes” facility.
Clayton and U2 have won numerous awards in their career, including 22 Grammy Awards, including seven times for Best Rock Duo or Group, and twice each for Album of the Year, Record of the Year, Song of the Year, and Best Rock Album.