After studying at Jesus College, Oxford and receiving a doctorate from the University of Oxford, he lectured at the University of Wales, Swansea from 1957 to 1978, rising to become Professor. In 1978, he returned to Oxford University as Jesus Professor of Celtic and also became a Professorial Fellow of Jesus College.
He began his academic career after completing his studies at Jesus College, Oxford, earning a Ph.D. from the University of Oxford. He then taught at the University of Wales, Swansea, from 1957 to 1978, advancing to become Professor. In 1978, he returned to Oxford University as a professor of Celtic studies and also became a Fellow of Jesus College.