Thomas McSweeney earned his B.A. from William & Mary, where he was a James Monroe Scholar. He continued his studies at Cornell University, where he earned a J.D. and a Ph.D. in medieval history. After completing his Ph.D., Professor McSweeney worked for two years as a visiting assistant professor at Cornell Law School, teaching property and legal history. During his time at Cornell, he won three awards for his teaching. In 2018, he received a Plumeri Award for Faculty Excellence from William & Mary. In 2019, the graduating class at William & Mary Law School presented him with the Walter Williams L. Award for Excellence in Teaching and in 2021 the first-year class presented him with the 1L Professor of the Year Award.

Professor McSweeney's research focuses on the early history of the common law. He is particularly interested in the ways the judges and lawyers of the thirteenth century taught and learned the law. His book, Priests of the Law: Roman Law and the Making of the Common Law's First Professionals (Oxford University Press 2019), which was awarded an honorable mention for the Selden Society’s David Yale Prize for an “outstanding contribution to the history of the law of England and Wales,” examines the ways in which thirteenth-century justices modelled their practices on those of the jurists of Roman law to make the case that the English common law was part of a pan-European legal culture. He visits the United Kingdom regularly for his research and has been awarded research grants to work at the Huntington Library, the British Library, and the British National Archives. He is currently a member of the board of directors of the Ames Foundation at Harvard Law School, which funds research in legal history, and in November of 2021 began a five-year term as an editor for the American Society for Legal History’s book series, Cambridge Studies in Legal History, at Cambridge University Press.

A devoted alumnus of William & Mary, Professor McSweeney has also written on the history of the college. His article "A University in 1693," co-authored with law students Katharine Ello and Elsbeth O’Brien, argues that William & Mary was awarded the status of a university in its 1693 charter, and thus has a claim to the title of oldest university in the United States. His current research project returns to the thirteenth century, and examines the texts that England’s earliest generations of lawyers used to learn the law.