Gagliardi was born in Naples. His first hit in Italy came in 1963 with "T'amo e t'amerò". In 1970, he had another big hit with the song "Settembre" and more hits followed in the early 1970s.
He achieved two second placings at the Sanremo Music Festival: in 1972 with "Come le viole" and in 1972 with "Come un ragazzino". His music declined in popularity in the 1980s and 1990s. His last entry at the Sanremo Music Festival was "L'alba" in 1993.