Randy Evan Barnett (born February 5, 1952) is an American legal scholar. He serves as the Patrick Hotung Professor of Constitutional Law at Georgetown University, where he teaches constitutional law and contracts, and is the director of the Georgetown Center for the Constitution.

After graduating from Northwestern University and Harvard Law School, Barnett tried felony cases as a prosecutor in the Cook County State's Attorney's Office in Chicago. A recipient of a Guggenheim Fellowship in Constitutional Studies and the Bradley Prize, Barnett has been a visiting professor at Penn, Northwestern and Harvard Law School.

In 2004, Barnett argued the medical marijuana case of Gonzalez v. Raich before the U.S. Supreme Court. In 2012, he was one of the lawyers representing the National Federation of Independent Business in its constitutional challenge to the Affordable Care Act in NFIB v. Sebelius. He blogs on the Volokh Conspiracy.

Barnett was born on February 5, 1952, in Chicago, Illinois, to a Jewish family. He was raised in Calumet City, Illinois, while attending synagogue in Hammond, Indiana, where he was president of the local Aleph Zadik Aleph (AZA) chapter and received his bar-mitzvah. After high school, Barnett was educated at Northwestern University, graduating in 1974 with a B.A. in philosophy. As an undergraduate, he was mentored by professor Henry Veatch in addition to being influenced by Murray Rothbard and the works of Ayn Rand.

After graduation, Barnett enrolled in Harvard Law School, receiving a J.D. in 1977. Barnett then returned to Chicago and worked as an Illinois state prosecutor for Cook County, Illinois.

Barnett spent the 1981–82 academic year as a research fellow at the University of Chicago Law School, then, in the fall of 1982, began his academic career as an assistant professor of law at the Chicago-Kent College of Law. In 1993, Barnett was hired as a professor of law at the Boston University School of Law. In 2006, Barnett left Boston and began teaching at the Georgetown University Law Center, where he currently remains.

In The Structure of Liberty, Barnett offers a libertarian theory of law and politics. Barnett calls his theory "the liberal conception of justice" and emphasizes the relationship between legal libertarianism and classical liberalism. He argues private adjudication and enforcement of law, with market forces eliminating inefficiencies and inequities, to be the only legal system that can provide adequate solutions to the problems of interest, power, and knowledge.

He discusses theories of constitutional legitimacy and methods of constitutional interpretation in Restoring the Lost Constitution.