He represented Bohemians and Sligo Rovers during his League of Ireland career. He was one of the most popular Bohemians players during the 1980s and scored 4 goals in 6 appearances in European competition during this time. He is most famous for scoring twice in a 3-2 win over Rangers in September 1984 in the UEFA Cup. Also scored twice against Dundee United in the same competition the following season.
He signed for Bohemians from schoolboy club Cambridge Boys and made his league debut in September 1981 against Sligo Rovers. He made 190 league appearances for Bohemians, scoring 33 goals before moving to Sligo at the end of the 1989/90 season.
O'Brien earned four caps for the Republic of Ireland U21 side.