O'Donnell was a pupil of Summerhill College in Sligo town and played rugby for the school team.

[7][8] O'Donnell's first start for the team also came in the Challenge Cup, when the province faced Newcastle Falcons away in the pool stages.

[9] He made a total of eight appearances for the senior team in his first academy season, playing four times in the Pro12 and Challenge Cup.

[6][7] At the beginning of the 2017–18 season, his final year in the academy, O'Donnell joined Buccaneers who had recently been promoted to Division 1A of the All- reland League.

[13] After the conclusion of the 2019 Super Rugby season, O'Donnell moved to New Zealand to join Mitre 10 Cup side Counties Manukau.

[16] O'Donnell was subsequently named in Nigel Carolan's squad for the 2015 Junior World Cup,[17] and played in four of the side's five matches in the tournament as they finished seventh overall.