Educated at St Peter's School in Roath, O'Neill played rugby for St. Peters RFC. O'Neill was first selected to play international rugby for Wales in a game against Scotland as part of the 1904 Home Nations Championship. Now playing for first class team Cardiff, and under the captaincy of Llwynypia's Willie Llewellyn, Wales won the game fairly easily, despite the rough play from Scotland's Bedell-Sivright. O'Neill was reselected for the very next game against Ireland, which Wales narrowly lost. O'Neill played in all three matches of the 1905 Championship which saw Wales win the tournament and the Triple Crown for the fourth time. O'Neill missed the next Wales game, the historic match against the first touring All Blacks, but was available for Cardiff against the same touring team ten days later. He also missed the Wales game against the first touring South African team, though was fit and well to represent both Glamorgan and Cardiff against the Springboks. Glamorgan lost 6-3, but the Cardiff team caused the biggest upset of the tour by outclassing the South Africans 17-0, only their second loss of the tour. O'Neill was back in the Welsh squad the next season playing two of the games in the 1907 Home Nations Championship, and was in all four matches of the 1908 tournament. Wales won all their matches and lifted their fifth Triple Crown, giving O'Neill his second trophy. In 1908, O'Neill turned his back on the amateur rugby union game by switching to professional rugby league. He joined Warrington, playing his first game for the club on 17 October 1908. After just two months as a professional rugby league footballer, he was selected for the Wales national league team, in an encounter with England at Broughton. He played one more international match, again against England, at Belle Vue, Wakefield in 1909. O'Neill played right-, i.e. number 10, in Warrington's 10-3 victory over Australia in the 1908–09 Kangaroo tour of Great Britain tour match during the 1908–09 season at Wilderspool Stadium, Warrington, Saturday 14 November 1908, in front of a crowd of 5,000, due to the strikes in the cotton mills, the attendance was badly affected, the loss of earnings meant that some fans could not afford to watch the first tour by the Australian rugby league team.
