On 9 March 2014, Leahy was an unused substitute when St. Kieran's College suffered a 2-13 to 0-13 defeat by Kilkenny CBS in the Leinster final.
[4] Leahy joined the Rower–Inistioge club at a young age and played in all grades at juvenile and underage levels.
On 27 October 2013, he won a Kilkenny Minor Championship medal after lining out at left wing-forward in a 2-09 to 1-07 defeat of O'Loughlin Gaels in the final.
He made his final appearance for the team on 20 June 2018 when he scored three points from midfield in a 1-17 to 3-13 defeat by Galway in the semi-final.
[12] Leahy lined out at left wing-forward for the All-Ireland final against Clare on 6 August 2016 and ended the game with a winners' medal after a 5-16 to 1-16 victory.
[15] Leahy was switched to left wing-forward on 1 July 2018 when Kilkenny drew 0-18 apiece with Galway in the Leinster final.
He was introduced as a substitute for Cillian Buckley at midfield but ended the game on the losing side after a 3-25 to 0-20 defeat.