O'Brien was drafted by Carlton with its second selection (No. 10 overall) in the
2017 national draft. He made his debut in
Round 4, 2018 against at
Blundstone Arena, and the following week was given a contract extension to the end of 2021. O'Brien played regular senior football in his first two seasons, appearing in 35 of 44 matches, before falling out of favour and playing only six across in 2020 and 2021. He was demoted from the club's senior list to its rookie list for the 2022 season. At the end of 2023 AFL season he was delisted from the Carlton Football Club. O'Brien was a member of
Wangaratta Rovers' 2024 and 2025
Ovens & Murray Football League premiership teams and won the league's best and fairest award, the Morris Medal in 2025. ==Statistics==