Jeffares took up his first academic appointment at the Department of English at the University of Groningen in 1947[2] and then moved to the University of Edinburgh in 1948. In 1951, at the very early age of 30, he was appointed to the Jury Chair of English at the University of Adelaide where he stayed until taking up the Chair of English at the University of Leeds in 1957. Finally, he moved to the University of Stirling in 1974. He retired as Emeritus Professor of English in 1985.
A specialist interest throughout his career was the life and works of W. B. Yeats, a subject upon which he was considered a leading authority.
He was the founder of the York Notes series of revision guides, which are still widely used by GCSE and A-Level students.
In 1978 he was made an honorary fellow of Trinity College Dublin.[4] On Australia Day 1988, Jeffares was appointed an Honorary Member of the Order of Australia, "for service to the study of Australian literature overseas".[5]
In 2013, an edition of the Yeats Annual was dedicated to him.[6]
as Author
Trinity College Dublin: Thirty-Four Drawings and Descriptions, Dublin: Alex, Thom & Co., 1944.
W. B. Yeats: Man and Poet, London: Routledge & Kegan Paul, 1949.
The Scientific Background: A Prose Anthology, London: Pitman, 1958. (with M. Bryn Davies)
Oliver Goldsmith, London: Longmans, Green & Co., 1959. (The British Council, Writers and Their Work no. 107)
The Poetry of W. B. Yeats, London: Edward Arnold, 1961. (Studies in English Literature no. 4)
George Moore, London: Longmans, Green & Co., 1965. (The British Council, Writers and Their Work no. 180)
Congreve: Incognita and the Way of the World, London: Edward Arnold, 1966. (Arnold's English Texts)