Geldof is widely recognised for his activism, especially anti-poverty efforts concerning Africa. In 1984, he and Midge Ure founded the charity supergroup Band Aid to raise money for famine relief in Ethiopia. They went on to organise the charity super-concert Live Aid the following year and the Live 8 concerts in 2005. Geldof currently serves as an adviser to the ONE Campaign, founded by fellow Irish humanitarian Bono. A single father, Geldof has also been outspoken for the fathers' rights movement. Geldof has been nominated for the Nobel Peace Prize, was granted an honorary knighthood by Queen Elizabeth II of the United Kingdom, and is a recipient of the Man of Peace title which recognises individuals who have made "an outstanding contribution to international social justice and peace", among numerous other awards and nominations.

Geldof was born in Dún Laoghaire, Ireland. His father, Robert, (also known as Bob) was the son of a Belgian immigrant, Zenon (sometimes mistakenly spelt Lenon) Geldof (born 1881), a Hotel Chef, and Amelia "Minnie" Falk (born 1876 in England). Zenon Geldof and Amelia Falk married in 1906 in St George's Square, and also had two daughters, Cleo Zenobie Geldof (born 1906 in Grantham), and May Geldof (born 1909 in Dublin) At the age of 41 Geldof's mother Evelyn complained of a headache and died shortly thereafter, having suffered a haemorrhage. Geldof attended Blackrock College, near Dublin, an exclusive private school whose Catholic ethos he disliked. He was bullied for his lack of rugby prowess and over his third forename - 'Zenon'. After work as a slaughter man, road navvy and pea canner, he started as a music journalist in Vancouver, Canada, for the weekly publication Georgia Straight.

Upon returning to Ireland in 1975, he became the lead singer of the band The Boomtown Rats, a rock group closely linked with the punk movement.

In 1978, The Boomtown Rats had their first No. 1 single in the UK with "Rat Trap", which was the first New Wave chart-topper in Britain. In 1979, the group gained international renown with their second UK No. 1, "I Don't Like Mondays". This was equally successful, as well as controversial; Geldof wrote it in the aftermath of Brenda Ann Spencer's attempted massacre at an elementary school across the street from her house in San Diego, California, at the beginning of 1979.

In 1980, The Boomtown Rats released the album Mondo Bongo. Its single "Up All Night" in 1981 was a hit in the U.S. and its video played on MTV with heavy rotation.[citation needed]

Geldof quickly became known as a colourful interviewee. The Boomtown Rats' first appearance on Ireland's The Late Late Show saw Geldof as deliberately brusque to host Gay Byrne and during his interview attacked Irish politicians and the Catholic Church which he blamed for many of the country's problems at the time, and responded to nuns in the audience that had tried to shout him down by saying they had "an easy life with no material worries in return for which they gave themselves body and soul to the church". He also criticised his old public school Blackrock College. The interview caused uproar across the country, making it impossible for the Boomtown Rats to play in Ireland again thereafter (apart from one gig at Lexlip Castle in 1980).

Geldof left the Boomtown Rats in 1986, to launch a solo career and publish his autobiography, Is That It?, which was a best-seller.

His first solo records sold reasonably well and spawned the hit singles "This Is The World Calling" (co-written with Dave Stewart of Eurythmics) and "The Great Song of Indifference". He also occasionally performed with other artists, such as David Gilmour of Pink Floyd and Thin Lizzy. A performance of "Comfortably Numb" with David Gilmour is documented in the 2002 DVD David Gilmour in Concert.

Geldof has also worked as a DJ for XFM radio. In 1998, he erroneously announced Ian Dury's death from cancer, possibly due to hoax information from a listener who was disgruntled at the station's change of ownership. The event caused music paper NME (who had been involved in a running feud with Geldof since his Boomtown Rats days primarily due to his disparagement of The Clash) to call Geldof "the world's worst DJ".

Along with U2's Bono, he has devoted much time since 2000 to campaigning for debt relief for developing countries. His commitments in this field, including the organisation of the Live 8 concerts, kept Geldof from producing any more musical output since 2001's Sex, Age & Death album.