Hayes was educated at Synge Street CBS ; University College, Dublin ; and the University of Oxford. Hayes came to St John's College, Oxford as an Overseas Scholar in 1955. At St John's, he was Fellow and Tutor from 1960 to 1987; and Principal Bursar from 1977 to 1987. Hayes was a University Lecturer from 1962 to 1985, and Professor from 1985 to 1987. Hayes was President of St John's College, Oxford from 1987 to 2001. He was Pro-Vice-Chancellor of the University of Oxford from 1990 to 2001.