Seán Duffy is a graduate of Trinity College Dublin, from which he also holds an M.Litt and a Ph.D. He is a Fellow of the College, where he has lectured since 1993 and is currently Professor in Medieval History. He has supervised 20 current or completed PhDs, has been been Head of Department, a member of the Board of Trinity College Dublin, and Secretary to the Fellows. He has written or edited more than 30 books and more than 40 peer-reviewed journal articles and book-chapters, has organized 27 conferences, given over 30 keynotes or international invited lectures, and served on 10 editorial or advisory boards. Since 1998 he has been Chairman of the Friends of Medieval Dublin, an influential not-for-profit advocacy organization and is much involved in pro bono consultative and advisory work on matters relating to history and heritage, particularly with Dublin City Council. Since 1999 he has organized an annual interdisciplinary conference on medieval Dublin, the proceedings of which are published each year by Four Courts Press. In 2013 he co-founded the Trinity Medieval Ireland Symposium, held biennially, the proceedings of which are published in a new Four Courts Press series, and he also a founder and organizer of prestigious biennial James Lydon Lectures in Medieval History and Culture, the volumes of which appear in a dedicated Cambridge University Press series.

 Seán Duffy specializes in the history of medieval Ireland and, in particular, three aspects: first, the political history of Ireland from the Viking Age to the Bruce Invasion; second, Irish relations with England, Scotland, and Wales in the same period; and third, the history and archaeology of medieval Dublin.