He is a graduate of "Harvard University, where he was awarded the degrees of "A.M. and "Ph.D. in Celtic Languages and Literatures in 1983 and 1985, respectively. He has also pursued studies at "Jesus College, Oxford, and the "University of Wales, Aberystwyth. He has taught Celtic Studies at Harvard University and "Boston College.
Since 1998, he has been senior research fellow or "Reader at the Centre for Advanced Welsh and Celtic Studies, University of Wales, where he has supervised a research project focusing on Celtic Languages and Cultural Identity. Two of the offshoots of this project are the five-volume Celtic Culture: A Historical Encyclopedia and An Atlas for Celtic Studies (2007).
He has published widely on aspects of early Irish and Welsh language, literature and history. His works include The Celtic Heroic Age (first published in 1994, 4th edition in 2003), in collaboration with "John Carey; The Gododdin of Aneirin (1997), an edition, translation and discussion of the early Welsh poem "Y Gododdin; and numerous articles published in books and journals. A grammar of "Old Welsh and a book on the historical "Taliesin are in the works.
In 2007, John Koch received a personal chair at the University of Wales.
Koch supervises (as Senior Fellow and Project Leader) the University of Wales Centre for Advanced Welsh & Celtic Studies Ancient Britain and the Atlantic Zone Project (Ireland, Armorica, and the Iberian Peninsula). In 2008, Koch gave the O'Donnell Lecture at Aberystwyth University titled People called Keltoi, the "La Tène Style, and ancient Celtic languages: the threefold Celts in the light of geography. In 2009, Koch published a paper Tartessian: Celtic from the Southwest at the Dawn of History detailing how the "Tartessian language may have been the earliest directly attested Celtic language with the Tartessian written script used in the inscriptions based on a version of a Phoenician script in use around 825 BC.