Leahy played his club hurling with his local Causeway club. He had his first major success in 1979 when he captured his first Kerry Senior Hurling Championship title. It was Causeway's first championship title since 1932. Leahy added three more county medals to his collection as Causeway completed a "four-in-a-row". He won a fifth county title in 1989.
In the early to mid 1970s, he played both club football and hurling in Cork. Firstly football for Clonakilty for eight years. He also spent a year with Newtownshandrum, with whom he won a Cork Intermediate Hurling Championship title in 1976.
Leahy made his senior inter-county debut with Kerry in 1977. Kerry were the reigning All-Ireland 'B' champions when he joined the panel, however, Kerry surrendered their title. Three years later, in 1980, Leahy took on the role of player-manager in 1980. It was the beginning of a successful period for Kerry. 1983 saw Leahy collect an All-Ireland 'B' medal as the men from 'the Kingdom' defeated London to take the title. He gave up the position of manager following that victory, however, he was reappointed as manager in 1985. The following year Leahy captured his second All-Ireland 'B' medal as player-manager. He retired from inter-county hurling in 1989.
While better known as a hurler, he also played with the Kerry senior football team during the mid 1970s.