On 3 May 2012 it was announced he had signed a two-year senior contract with Perth Glory[2]
Sydney FC
On 25 May 2015, O'Neill signed a two-year contract with Sydney FC.[3]
O'Neill scored his first A-League goal in the Sydney Derby on Saturday 8 October 2016 by bending a free kick around the wall from just outside the penalty area into the top right corner. He scored his second goal of the season, also from a free kick against Melbourne City on Friday 24 February 2017 by curling the ball over the wall and into the top corner.[4]
Following performances which made him a key member of the starting squad, Sydney FC re-signed O'Neill for another two years on 13 December 2016.[5]
On 26 March 2017, O'Neill scored his third goal for Sydney FC away at Perth Glory, with a low and hard shot from outside the box, as the Sky Blues ran out 3–0 winners and secured the premiers plate.[6]
Pohang Stelers
On 13 January 2020, it was announced that K League 1 side Pohang Steelers had reached an agreement with Sydney for the transfer of O'Neill.[7] The fee is believed to be between $250,000 and $300,000 AUD, with the player agreeing to sign a two-year deal.[8][9]
On 1 July 2021, it was announced that O'Neill would return to his hometown club on a three-year deal.[10] Following the departure of Diego Castro, O’Neill was announced on 28 October as captain for the 2021/22 season.[11]
Newcastle Jets
In June 2022, O'Neill signed for Newcastle Jets for the next two seasons.[12]
Return to Perth again
On 31 May 2024, Perth announced O'Neill had re-signed for the club once again, on a two-year contract.[13]