John M. Walker, Jr. is a United States Circuit Judge of the United States Court of Appeals for the Second Circuit. At the time of his appointment to the Court in 1989, he was a United States District Judge in the Southern District of New York.

Judge Walker received his B.A. degree from Yale University in 1962, and his J.D. degree from the University of Michigan Law School in 1966.

Judge Walker served in the U.S. Marine Corps Reserves from 1963 until 1967. From 1966 until 1968, he was State Counsel to the Republic of Botswana under the aegis of an Africa-Asia Public Service Fellowship. Judge Walker was a private law practitioner in New York from 1969 to 1970. From 1970 to 1975 he served as an Assistant United States Attorney in the Criminal Division, Southern District of New York. In 1975 he returned to private law practice with the New York firm of Carter, Ledyard & Milburn, where he was initially an associate and later a partner. In 1981 Judge Walker became Assistant Secretary of the Treasury, responsible for policy in law enforcement, regulatory, and trade matters, and with oversight of the Customs Service, Secret Service, Federal Law Enforcement Training Center, Bureau of Alcohol, Tobacco and Firearms, and the Office of Foreign Assets Control. Judge Walker remained in this position until 1985, when he became a United States District Judge for the Southern District of New York.

Judge Walker has served as Special Counsel to the U.S. Administrative Conference (1987-1992); president of the Federal Judges' Association (1993-1995); and member of the Budget Committee of the Judicial Conference of the United States (1991-1999). He has been a Visiting Lecturer at Yale Law School since 2000; an Adjunct Professor at NYU Law School since 1996; and Director and on the faculty of NYU Law School's Institute of Judicial Administration and Appellate Judges Seminar since 1992. Judge Walker has also been a Director of the U.S. Association of Constitutional Law since 1997. Judge Walker is married with a daughter and three stepsons.