Mulcahy made his senior hurling championship debut for Cork on 26 June 1983 when he came on as a substitute in a 1–14 to 1–12 Munster semi-final replay defeat of Limerick. He was added to the starting fifteen at right corner-forward for the subsequent provincial decider against Waterford. Mulcahy scored a point and collected his first Munster medal following a huge 3–22 to 0–12 victory. The All-Ireland final on 4 September 1983 was a replay of the previous year with Cork hoping to avenge the defeat by Kilkenny. Billy Fitzpatrick was the star with ten points, giving Kilkenny a 2–14 to 1–9 lead with seventeen minutes left, however, they failed to score for the remainder of the game. A stunning comeback by Cork just fell short and Mulchay's side were defeated by 2–14 to 2–12.