Morris read modern history at Jesus College, Oxford, from 1932 to 1935, and served in the Army during the Second World War.
He was one of the writers, along with A. H. M. Jones and J. R. Martindale, of The Prosopography of the Later Roman Empire, a biographical dictionary of the years 284–641, the first volume of which was published in 1971.
Although popular with the public, the book was heavily criticised in professional historical circles, severely damaging Morris's academic reputation in the eyes of many of his peers.
David Dumville launched a famously scathing attack on Morris's methodology;[5] and while one of the most influential reviews of the book, by D. P. Kirby and J. E. Caerwyn Williams, described it as "an outwardly impressive piece of scholarship", it went on to argue that this apparent scholarship "crumbles upon inspection into a tangled tissue of fact and fantasy which is both misleading and misguided".
[6] Others, such as James Campbell, were more generous, but still considered that the Age of Arthur was so misleading and full of problems that it was really only of use to professional historians who could sort the interesting ideas from the flights of fantasy.