O'Brien first joined the youth set-up at
Accrington Stanley at the age of eight, and went on to captain the under-18s to the fourth round of the
FA Youth Cup in
2021–22. He signed his first one-year professional contract in June 2022. On 3 December 2022, he joined
Northern Premier League Premier Division club
Radcliffe on a one-month loan. He scored on his debut later that day, in a 2–2 draw at
Matlock Town. On 13 February 2023,
Radcliffe extended his loan by a further 2 months. On 10 May 2024, O'Brien extended his contract at Accrington Stanley by two years. ==International career==