O'Brien was released by Warrington at the end of the 2015 season, alongside teammates Joel Monaghan and Roy Asotasi, as the club continue their on and off-field changes.

[9] O'Brien's time at Castleford was cut short when he was recalled by Warrington following an injury to half-back Lee Briers.

O'Brien helped the Saints to a famous 22–16 victory over arch rivals Wigan Warriors by kicking 2 goals.

In May 2015, O'Brien played for the North Wales Crusaders in League 1 through their dual registration arrangement with Warrington.

[citation needed] O'Brien joined the Salford Red Devils for the 2016 season and was assigned squad number 14.

[12] In the Million Pound Game against Hull KR, he scored an incredible near-halfway drop goal in golden-point extra time to secure Salford's place in Super League.

On 12 March 2018, having made 4 appearances and scored 1 try and 9 goals in the 2018 season, it was announced that O'Brien would leave Salford to join Toronto Wolfpack with immediate effect.

This included 2 conversions in the Championship play-off final victory over Featherstone Rovers, to win promotion to Super League.

After Toronto were forced to withdraw from the 2020 competition, players were allowed to find new clubs for the rest of the season so he joined Castleford on loan.

[19] He arrived as a direct replacement for full-back Jordan Rankin who had been released during the season suspension to allow him to return to Australia.

[20] Head coach Daryl Powell likened his abilities to those of Castleford fan favourite Luke Dorn: "he can see things very quickly, his communication is great, he has got pace and his decision-making is excellent.

[citation needed] Castleford announced the permanent signing of O'Brien on a three-year deal on 15 November 2020, after Toronto were denied readmission to Super League.

[24] In Castleford's round 3 Challenge Cup match against Hull KR, O'Brien kicked a 99th-minute drop goal to secure a victory for the Tigers in the fourth period of golden point extra time.

[27] On 12 August 2023, O'Brien played for Leigh in their 17-16 Challenge Cup final victory over Hull Kingston Rovers.

[28] O'Brien played 27 games for Leigh in the 2023 Super League season as the club finished fifth on the table and qualified for the playoffs.

[29] O'Brien played 19 games for Leigh in the 2024 Super League season which saw the club finish fifth on the table.

[30] In round 1 of the 2025 Super League season, O'Brien kicked the winning drop goal for Leigh as they defeated rivals Wigan 1-0 in golden point extra-time.