From 1963 to 1966 he studied for a B.A. in English; he then continued with several postgraduate studies until 1969. In 1970 he obtained a Ph.D. from Cambridge University for a dissertation which was an edition of Ælfric's Second Series of Catholic Homilies under the supervision of Professor P. A. M. Clemoes.
His academic appointments include:
- 1969-1972: Junior Research Fellow, Pembroke College, Cambridge
- 1970-1971: Visiting Assistant Professor, Department of English, Cornell University
- 1972-75: University Lecturer, Department of English Language, Liverpool University
- 1976-91: Fellow and lecturer in English, Exeter College, Oxford, and CUF Lecturer in the Faculty of English, Oxford University
- 1991-2013: Rawlinson and Bosworth Professor of Anglo-Saxon in the University of Oxford, and professorial fellow of Pembroke College, Oxford.
- Ælfric's Catholic Homilies: the Second Series, Text (Early English Text Society, Supplementary Series; 5.) Oxford: University Press, 1979
- The Making of Piers Plowman. London, 1990
- The Cambridge Companion to Old English Literature; edited with M. Lapidge. Cambridge: University Press, 1991
- From Anglo-Saxon to Early Middle English: studies presented to E. G. Stanley; edited with D. Gray and T. Hoad. Oxford, 1994
- Ælfric's Catholic Homilies: the First Series, Text; ed. P. Clemoes. (Early English Text Society, Supplementary Series; 17.) Oxford: University Press, 1997
- Ælfric's Catholic Homilies: Introduction, Commentary and Glossary. (Early English Text Society, Supplementary Series; 18.) Oxford: University Press, 2000
- The Old English Boethius: an edition of the Old English versions of Boethius’s "De Consolatione Philosophiae"; edited with S. Irvine. 2 vols. Oxford: University Press, 2009