O'Shea made his debut on the inter-county scene at the age of sixteen, when he was selected for the Kerry under-21 team. He enjoyed one championship season with the under-21 side, winning an All-Ireland medal in 1996. By this stage, he had also joined the Kerry senior team, making his debut during the 1995-96 league. Over the course of the next three seasons, O'Shea won one All-Ireland medal in 1997. He also won back-to-back Munster medals and one National Football League medal. All of these titles were won as a substitute.
Subsequent to relocating to Australia, O’Shea embarked upon a career in Australian Rules Football playing the "AFL 9s" version of the game. However, an inability to adapt to the oval ball and a run of calf injuries has limited his impact at this level. He has concentrated instead on his business and community service efforts.
