O'Leary-Hayes played in all grades of hurling with Midleton CBS Secondary School before progressing onto the college's senior team.
On 15 December 2016, he was at full-back when Midelton CBS defeated St. Colman's College from Fermoy by 0-11 to 0-10 to win the Dr. O'Callaghan Cup.
[1] O'Leary-Hayes joined the Midleton club at a young age and played in all grades at juvenile and underage levels.
[8] He was selected at centre-back when Cork faced Tipperary for a second time in the All-Ireland final on 24 August 2019 but spent much of the game at left corner-back.
[9] O'Leary-Hayes was called up to the Cork senior panel in late 2018 before making his debut on 2 January 2019 when he came on as a substitute in a 1-24 to 1-18 defeat by Waterford in the Munster League.