[1] O'Brien first played for the Nemo Rangers club as a five-year-old, however, he first came to prominence as a schoolboy with Coláiste Chríost Rí with whom he won the Hogan Cup in 1987.
That same year he made his senior debut with Nemo and went on to win three All-Ireland Club Championships over the following 15 seasons.
[2] O'Brien first appeared on the inter-county scene as a defender with the Cork minor team that lost successive All-Ireland finals.
By this stage O'Brien had already joined the Cork senior football team and won the first of six Munster Championship titles in his debut season in 1988.
O'Brien was also selected for Munster and was manager of the Nemo Rangers team that secured the 2015 Cork County Championship.