Cummins made his debut on the inter-county scene at the age of sixteen when he was picked on the Cork minor football panel before later joining the hurling panel. He was a Munster medal winner in both codes in 1966, however, All-Ireland success in this grade eluded him. He subsequently progressed onto the Cork under-21 teams, winning back-to-back All-Ireland medals as a hurler in 1968 and 1969. Cummins made his senior debut for Cork during the 1967-68 football league, before becoming a regular on the Cork hurling team the following year. Over the course of the next fifteen years he used his physical attributes to telling effect by punching many fine points in football and "catching high" and delivering many winning scores in hurling. As a hurler Cummins is credited with redefining and revolutionising the full-forward position throughout the 1970s. He was, at first, seen as the antithesis of what a full-forward should be, however, he did use the skills and space that were available to him and, in time, he became a deadly marksman in front of goal. He won his first All-Ireland medal as a hurler in 1970, added a second winners' medal to his collection in 1973 as a footballer before winning three hurling championships in-a-row from 1976 to 1978. Cummins also won a total of twelve Munster medals across both codes, including a remarkable eleven-in-a-row, and three National Hurling League medals. The All-Ireland-winning captain of 1976, he also collected five All-Star awards between 1971 and 1977 and is one of only four players to have won awards in both codes. Cummins played his last game for Cork in September 1982.