Justice Mariano-Florentino Cuéllar began serving on the California Supreme Court in January 2015. Previously he was the Stanley Morrison Professor of Law and Professor (by courtesy) of Political Science at Stanford University. A Stanford faculty member since 2001 and a fellow of the American Academy of Arts and Sciences, Cuéllar is a scholar of public law and institutions whose books and articles explore problems in administrative law and legislation, cyberlaw, criminal justice, public health law, international law and security, immigration, and the history of institutions.

A naturalized U.S. citizen born in Northern Mexico, Cuéllar graduated from Calexico High School in California’s Imperial Valley. He received a B.A. from Harvard magna cum laude, a J.D. from Yale Law School, and a Ph.D. in Political Science from Stanford. He began his career at the U.S. Treasury Department's Office of Enforcement and clerked for Chief Judge Mary M. Schroeder of the U.S. Court of Appeals for the Ninth Circuit. He is married to Judge Lucy H. Koh of the U.S. District Court for the Northern District of California.

In 2019 he was elected to serve as a member of the Harvard Corporation and his term will begin on July 1.