Professor Thomas Owen Clancy is an American academic and historian who specializes in the literature of the Celtic Dark Ages, especially that of Scotland. He did his undergraduate work at New York University, and his Ph.D at the University of Edinburgh. He is currently at the University of Glasgow, where he was appointed Professor of Celtic in 2005.

In 2001, Clancy argued that St. Ninian was a Northumbrian spin-off of the name Uinniau (Irish St. Finnian), the Irish missionary to whom St. Columba was a disciple, who in Great Britain was associated with Whithorn. He argued that the confusion is due to an eighth century scribal spelling error, for which the similarities of "u" and "n" in the Insular script of the period were responsible.