Inter-county
O'Neill first lined out with Cork in the minor grade in 2003. In the following season, 2004, he won his first Munster medal as Cork ended Tipperary's hopes of four-in-a-row with a 2-13 to 3-8 victory.[3]
The following year O'Neill was a member of the Cork under-21 team. He won a Munster Under-21 Hurling Championship medal in his debut year, as Cork defeated Tipperary by 4-8 to 0-13.[4]
Two years later and O'Neill was appointed captain of the Cork under-21 team. He won a second Munster medal on that occasion following a 1-20 to 0-10 win over Waterford.[5]
By 2005 O'Neill's performances for the Cork minor and under-21 teams brought him to the attention of the senior selectors. He was a member of the extended panel during Cork's All-Ireland victory. He won a Munster medal in 2006 as an unused substitute.
On 17 June 2007 O'Neill made his senior championship debut in a 5-15 to 3-18 Munster semi-final defeat by Waterford. The following few seasons saw Cork go into decline.[citation needed] In 2011, O'Neill was appointed captain of the team.[6]
O'Neill lined out in his second Munster decider in 2013, however, Cork faced a 0-24 to 0-15 defeat by Limerick.[7] On 8 September 2013 he lined out against Clare in his first All-Ireland final. Three second-half goals through Conor Lehane, Anthony Nash and Pa Cronin, and a tenth point of the game from Patrick Horgan gave Cork a one-point lead as injury time came to an end. A last-gasp point from corner-back Domhnall O'Donovan earned Clare a 0-25 to 3-16 draw.[8] The replay on 28 September saw Clare's Shane O'Donnell score a hat-trick of goals in the first nineteen minutes of the game. Patrick Horgan was top scorer for Cork, however, further goals from Conor McGrath and Darach Honan secured a 5-16 to 3-16 victory for Clare.[9]
In 2014, O'Neill won his first Munster Senior Hurling Championship medal on the field of play as goals by Séamus Harnedy and Paudie O'Sullivan gave Cork a 2-24 to 0-24 victory over Limerick.[10]