Educated at Lewis School Pengam, along with John Dawes, he was capped five times for Wales as a prop between 1967 and 1968. 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.
He played club rugby for Cardiff. He is currently living in Australia.