O'Halloran played school football for his team at St. Bernard's College in Melbourne, where he won the Herald Sun Shield and the Neale Daniher Award.[5][6] He also captained the Western Jets in the NAB League for the 2018 season,[5] while playing for them in the 2017 and 2018 seasons, where he picked up a total of 31 goals.[7] O'Halloran also represented and captained Vic Metro in the AFL Under 18 Championships for the 2018 season.[8][5]
^The 2020 season was played with 17 home-and-away matches per team (down from 22) and 16-minute quarters with time on (down from 20-minute quarters with time on) due to the impact of the COVID-19 pandemic.