Known as the "white Zulu", he was a vocal critic of the apartheid government which ruled until 1994.
The British-born musician, who uniquely blended western and Zulu music, was diagnosed with cancer in 2015.
His best known hit Asimbonanga, released in 1987, was dedicated to Nelson Mandela.
Meaning "We have not seen him" in Zulu, the song was one of the first to openly call for Mandela's release.
At the time, the future first black president of South Africa was still in jail and considered a threat to the apartheid state.
Clegg - a white man who learnt to speak and sing in Zulu - became a symbol of democratic South Africa and was chosen to sing at Nelson Mandela's memorial service in 2013.