Minor and under-21
O'Halloran first lined out for Waterford as a member of the minor team during the 2008 Munster Championship. He made his first appearance on 25 June when he scored 0-02 from left wing-forward in a 4–13 to 1–06 defeat by Cork.[7]
O'Halloran was also eligible for the minor grade in 2009. He was at centre-forward when Waterford qualified for a Munster final-meeting with Tipperary on 12 July. O'Halloran scored a point from play and collected a Munster Championship medal following the 0–18 to 1–13 victory.[8]
On 19 July 2012, O'Halloran made his only appearance for the Waterford under-21 team. He scored a point from right wing-forward in a 2–22 to 0–09 defeat by Clare in the Munster Championship.[9]
Senior
O'Halloran joined the Waterford senior team for the 2010 Munster Championship having just completed his Leaving Certificate. On 11 July, he was an unused substitute when Waterford drew 2-15 apiece with Cork in the Munster final.[10] O'Halloran also started the replay on the bench but was introduced as a 49th-minute substitute for Séamus Prendergast. He scored a point from play and collected a Munster Championship medal following the 1–16 to 1–13 victory.[11]
On 5 February 2011, O'Halloran lined out at centre-forward when Waterford defeated Cork by 0–21 to 0–16 to win the pre-season Waterford Crystal Cup.[12] In March 2011, he tore his hamstring tendon and was ruled out for the rest of the season. After returning to the panel in 2012, O'Halloran tore ligaments in his ankle and missed the entire season for a second successive year. O'Halloran said: "I suppose I would have had the name of being injury prone but it was actually only two major injuries and they took it out of the body. It was hard to get back on the wagon after them."[13]
On 3 May 2015, O'Halloran was named at right corner-forward but started the game on the bench when Waterford faced Cork in the National League final. He scored a point from play after being introduced as a 58th-minute substitute for Colin Dunford and collected a winners' medal following the 1–24 to 0–17 victory.[14] On 12 July 2015, O'Halloran was an unused substitute when Waterford were beaten for the fourth time in six seasons by Tipperary in the 2015 Munster final.[15]
On 1 May 2016, O'Halloran was introduced as a 63rd-minute substitute for Austin Gleeson when Waterford drew 0-22 apiece with Clare in the National League final.[16] He also started the replay on the bench but once again scored a point after being introduced as a substitute in the replay, which Waterford lost by 1–23 to 2–19.[17] On 10 July, O'Halloran came on as a substitute for Pauric Mahony in the 60th minute of the Munster final, with Waterford eventually losing by 5–19 to 0–13.[18]
On 3 September 2017, O'Halloran was named on the bench when Waterford faced Galway in the All-Ireland final. He came on as a 48th-minute substitute for Jake Dillon at left wing-forward and scored a point from play in the 0–26 to 2–17 defeat.[19]
O'Halloran played his last game for Waterford on 8 June 2019 in a 2–30 to 2–17 defeat by Cork in the Munster Championship.[20] He announced his retirement from inter-county hurling two days later.[21]