Thomas J. Brennan

A scholar at the intersection of tax law and financial economics, Thomas J. Brennan is the Stanley S. Surrey Professor of Law at Harvard Law School. His research uses tools from mathematics and financial economics to analyze tax law and develop proposals for reform of the taxation of capital income, financial instruments, and strategic tax planning. He also conducts empirical research on the behavior of firms and markets in response to tax law changes, including the repatriation decisions of multinational corporations.

Professor Brennan’s research spans an unusually broad range of disciplines. In addition to tax law and policy, his published work addresses the mathematical foundations of portfolio theory and asset pricing, the evolutionary origins of economic behavior and bounded rationality, and the relationship between macroeconomic conditions and judicial decision-making. His articles have appeared in leading law reviews and peer-reviewed journals including Management Science, the Proceedings of the National Academy of Sciences, the Texas Law Review, and the Yale Journal on Regulation. He has co-authored a number of articles with Andrew W. Lo of the MIT Sloan School of Management on topics spanning financial economics, evolutionary theory, and financial regulation. Professor Brennan is a co-author of Federal Income Taxation of Corporations and Partnerships (Aspen Publishers, 7th ed. 2025), a widely used law school casebook, and Federal Corporate Taxation (Foundation Press, 9th ed. 2026), a comprehensive teaching text on corporate taxation.

Professor Brennan’s research has been featured in the New York Times and Bloomberg, among other media. His empirical work on corporate tax repatriation was cited in a Majority Staff Report of the Permanent Subcommittee on Investigations of the United States Senate.

Professor Brennan has received several teaching awards, including the Robert Childres Memorial Award for Teaching Excellence and the Outstanding First-Year Course Professor Award, both from Northwestern University School of Law, and the Faculty Impact Award from the Northwestern University Kellogg School of Management.

Before joining the Harvard faculty, Professor Brennan held academic appointments as the Justin W. D’Atri Visiting Professor of Law, Business and Society at Columbia Law School; as Professor of Law at Northwestern University School of Law, where he also held a courtesy appointment in Finance at the Kellogg School of Management; and as Visiting Scholar in the Laboratory for Financial Engineering at the MIT Sloan School of Management. Before entering the academy, he practiced tax law as an associate in the Tax Department at Cravath, Swaine & Moore LLP, and worked as a strategist in the Capital Markets Strategies group at Goldman, Sachs & Co. He is admitted to the practice of law in the State of New York.

Professor Brennan received an A.B. in mathematics, summa cum laude, from Princeton University, where he was awarded the George B. Covington Prize, Princeton’s Senior Prize in Mathematics. He received an A.M. and a Ph.D. in mathematics from Harvard University and a J.D., cum laude, from Harvard Law School.

Professor Brennan is an elected fellow of the American College of Tax Counsel and an elected member of the American Law Institute. He consults on matters involving tax law, financial instruments, and related areas of law and finance.