Before his senior year of high school, O'Brien was given the option to leave Thayer Academy early and join the Youngstown Phantoms in the United States Hockey League.
[3] Following graduation from Thayer Academy, O'Brien joined the Providence College Friars in the Hockey East of the National Collegiate Athletic Association (NCAA).
Opting to enter the NCAA transfer system and end his tenure with Providence, O'Brien agreed to join Canadian junior team, the Penticton Vees of the British Columbia Hockey League (BCHL), for the 2019–20 season.
[5] He later agreed to join fellow Hockey East competitor in Boston University for the 2020–21 season prior to his tenure in the BCHL.
As a free agent from the Marlies, O'Brien was signed to a one-year AHL contract with the Charlotte Checkers on July 2, 2024.