Adam attended private boarding school(lives nearby) St. Columba's in Rathfarnham, but hated it. Being a bit of a hippie, Adam's freewheeling personality was at odds with the structured environment. He later switched to Mount Temple Comprehensive School, Ireland's first ecumenical school, where he met his U2 bandmates Paul "Bono" Hewson, Dave "The Edge" Evans and Larry Mullen Jr. Mullen had posted an advertisement for musicians. Adam ignored it at first, believing it was a school-sponsored event. When he discovered that it wasn't, he showed up at the first practice, which also included Dik Evans, Dave's older brother. When Dik Evans left, the fledgling band that would become U2 was created. They were known first as Feedback, then The Hype. He also served as the band's first manager before Paul McGuinness, a more experienced manager, was hired.

Adam's ambiguous religious beliefs caused a rift with his three outspoken Christian bandmates which peaked between the time of their second album, October (1981) and their third album, War (1983). Reportedly, Clayton was being treated as a bit of an outsider until manager Paul McGuinness came to his aid. To smooth over the rift, Adam was asked to be Bono's best man at his wedding.

In 1986, U2 recorded what is considered by many to be their first masterpiece: 1987's The Joshua Tree album, at Danesmoate House. Adam later bought the home for approximately €380,000. It is hidden away behind Taylors Pub on Kellystown Road, Rathfarnham.

Adam's name made world headlines in August 1989 when he was arrested in the car park of the Blue Light pub in Barnacullia, Dublin, and charged with possession of a small amount of marijuana. He avoided a conviction by making a sizable cash donation to charity. Adam has battled alcohol abuse, culminating in him being too unwell to play with the band in Sydney in 1993; the only performance missed by a U2 member since the late-1970s. He no longer drinks.

In the early 90's Adam was involved in a relationship with supermodel Naomi Campbell and at one stage they were even engaged. The relationship, however, eventually failed.

For many years, Adam appeared to be the confirmed bachelor of the group while his three bandmates were married or involved in steady relationships. But on 10 April 2006, the band's website, U2.com, announced Adam's engagement to Suzanne "Susie" Smith, a record company executive based in London and a former assistant to U2 manager Paul McGuinness. The couple, who had dated for 10 years before making this commitment, were planning to marry in the summer of 2007 but they split up in February 2007.

(bio from wikipedia)