O'Brien began his career playing rugby union for Marlborough between 1919 and 1921.
[2] In that game he lined up alongside fellow future dual-international Charles Fitzgerald.
He immediately was selected for the North Island side and subsequently the All Blacks tour of New Zealand and South Wales.
Returning to Auckland, O’Brien played his first game for the union late in the 1922 season.
He played for Auckland and made the New Zealand national rugby league team for three tests against the touring Great Britain Lions side that year.