O’Riordan first came to prominence with the Cork senior hurlers in the mid-1940s. He won his first Munster title in 1946 before later collecting his first All-Ireland medal following a victory over Kilkenny in the championship decider. The following year O’Riordan won a second Munster title, however, Kilkenny gained revenge by defeating Cork in that year’s classic All-Ireland final. Cork failed in the Munster Championship for the next four years, however, the team bounced back in 1952 with O’Riordan adding a third Munster medal to his collection. He later collected his second All-Ireland medal following a victory over Dublin in the championship decider. Cork continued their winning ways in 1953 with O’Riordan adding a National Hurling League medal to his collection. He later collected his fourth Munster title before later winning a third All-Ireland medal following Cork’s defeat of Galway in one of the dirtiest All-Ireland finals ever. In 1954 Cork made it three-in-a-row by capturing another set of Munster and All-Ireland titles. Once again O’Riordan played a key role in helping Cork to maintain this dominance and he collected a fourth Celtic cross medal in the process.