Best known as the lead singer and harmonica player of the Yardbirds. After the Yardbirds broke up, Relf formed the acoustic duo Together with fellow Yardbird Jim McCarty, followed by Renaissance which also featured his sister, singer Jane Relf, then hard rock group Armageddon. Relf also produced tracks for bands such as the acoustic world music group Amber, Saturnalia and Medicine Head, with whom he played bass guitar.

Relf was 33 when he died from electrocution, at his home, while playing his improperly earthed electric guitar. At the time, Relf was rehearsing new material for the regrouping of the original Renaissance line-up, called Illusion.