A faculty member at Western since 1988, Professor Kostal teaches Legal History and Torts. Professor Kostal's research interests are focused in the field of modern Anglo-American legal history. He is the author of Law and English Railway Capitalism 1825-1875 (Oxford University Press, 1994), A Jurisprudence of Power: Victorian Empire and the Rule of Law (Oxford University Press, 2005), and a number of published writings in Legal History and Tort Law.

In 2019, Harvard University Press published Professor Kostal's monograph book, Laying Down the Law: The American Legal Revolutions in Occupied Germany and Japan, awarded the 2020 Phillip Reid Prize of the American Society for Legal History. With Erika Chamberlain, Professor Kostal is currently completing a book project on the social history of Canadian tort law and litigation, 1945-1995.