O'Brien first came to prominence at juvenile and underage levels with the Newtownshandrum club before joining the club's senior team in 2019. As a schoolboy at CBS Charleville he also lined out in various hurling competitions including the Harty Cup. O'Brien first appeared on the inter-county scene as a half back on the Cork under-17 team that won the one-off All-Ireland Under-17 Championship in 2017. A year with the Cork minor team followed before he won consecutive All-Ireland Under-20 Championships in 2020 and as team captain in 2021. O'Brien joined the Cork senior hurling team as a member of the extended training panel in 2021 and made his debut in the National League against Limerick.
