O'Brien was a physically tough defender who usually played at centre half back. He was Carlton's captain in 1924, and was a member of Carlton's back-to-back premierships in 1914 and 1915.
In 1925, he commenced the season as Carlton's playing coach but lasted only two games due to disagreements within the team. He left to join Footscray during their inaugural VFL season but played just 15 games for the club.
Victoria 13.16 (94) defeated Tasmania 7.13 (55), at North Hobart Oval, 7 August 1924, crowd: 8,000
Victoria 15.13 (103) defeated Western Australia 14.11 (95), at North Hobart Oval, 9 August 1924, crowd: 15,687 Victoria 14.26 (110) defeated New South Wales 4.6 (30), at North Hobart Oval, 12 August 1924, crowd: 350
Victoria 17.16 (118) defeated South Australia 9.11 (65), at North Hobart Oval, 15 August 1924, crowd: 12,876