At club level he played with Glen Rovers and St. Nicholas' and was also a member of the Cork senior teams as a dual player.
[2] Three years later he claimed a second winners' medal, this time lining out at left wing-back, when Youghal were beaten in the 1972 final.
[4] Glen Rovers lost the 1973 Cork SHC final to Blackrock and again faced defeat by the same opposition in 1975 when O'Brien was team captain.
His one-year tenure with the minors was a successful one as Cork completed a double of All-Ireland victories after defeats of Wexford and Laois.
[13] O'Brien was still eligible for the under-21 grade when he made his Cork senior football team debut in the 1969-70 National League.
[16] O'Brien ended his dual status shortly after this win and committed solely to the Cork senior hurling team.
[17] After being dropped off the panel shortly afterwards he earned a recall a year later and was an unused substitute when Cork beat Wexford in the 1977 All-Ireland final.