O'Shea was selected for the 1968 British Lions tour to South Africa and played in the first international against South Africa. In the match against Eastern Transvaal at Springs he became the first Lion ever to be sent off for foul play, after throwing a punch.[2] He was then hit by a spectator while walking off which resulted in a brawl.[3] Later in the tour while playing against Rhodesia, he became the first Lions prop to score two tries in a game.[3]
O'Shea played club rugby for Cardiff between 1963 to 1970, becoming club captain in his final year.[3] In total he played 213 games for them and scored 19 tries.[4]