Day was the first lead singer for Iron Maiden from 1975 to 1976. On the Iron Maiden The Early Days DVD it was mentioned that Day was sacked because he did not have enough stage charisma. He was replaced by Dennis Wilcock.
He later formed a band called More that played at the Donington Monsters of Rock Festival in 1981. He was lead singer of Wildfire in 1983 to 1984. He recorded a live album at the Marquee Club in London as lead singer of Sweet in 1986. He has lived in Australia since 1986 and is the lead vocalist of two bands from Newcastle, New South Wales. He performs covers of rock songs with the band Defaced and sang and wrote for Crimzon Lake, now disbanded, an unsigned hard rock band.