After attending Liston College, O'Neil started his career with the Marist Saints before making the Waitakere City Raiders side in the Lion Red Cup.
In 1997 O'Neill moved to England and joined the St. Helens in the Super League competition where he gained the club's highest tackler and most offloads in the 1997 season.
O'Neill went on to play in 126 games for the Saints, including being involved in the side that won the 1997 Challenge Cup and 1999's Super League IV title.
Having won the 1999 Championship, St. Helens contested in the 2000 World Club Challenge against National Rugby League Premiers the Melbourne Storm, with O'Neill playing at prop forward in the loss.
In 2001 O'Neill joined the Wakefield Trinity Wildcats but at the end of the 2001 season was signed by Widnes Vikings to boost their forward pack.