John Joseph O'Neill (born 26 August 1957) is the rhythm guitarist and principal songwriter of the punk rock/new wave band The Undertones.
O'Neill, along with his younger brother Vincent and friends Feargal Sharkey, Michael Bradley and Billy Doherty, founded The Undertones in 1975, although Vincent O'Neill was replaced the following year with his younger brother Damian O'Neill, who became the band's lead guitarist.
John O'Neill wrote the majority of the band's singles and a number of album tracks (occasionally collaborating with his brother Damian or Michael Bradley).
Undertones songs written by John O'Neill include the singles "Teenage Kicks", "Jimmy Jimmy", "Here Comes The Summer" and "You've Got My Number", and such notable album tracks as "When Saturday Comes" and "You're Welcome".
After releasing four albums and thirteen singles, The Undertones disbanded in 1983; they reformed in November 1999.
Despite some positive reviews in the music press they only had one notable chart appearance and disbanded shortly after the release of their only album in 1998.