Louis Henkin was a clerk to Judge Learned Hand and to Justice Felix Frankfurter. He served as the book review editor for the Harvard Law Review. After a period as consultant to the United Nations Legal Department, Professor Henkin served with the Department of State from 1948 to 1956 in the U.N. Bureau and in the Office of European Regional Affairs (NATO). He went on to represent the U.S. on the committee drafting the Convention on the Status of Refugees and to serve on U.S. delegations to the U.N. and to international conferences.

Professor Henkin then spent a year at Columbia from 1956-1957 as associate director of the Legislative Drafting Research Fund while writing his first book, Arms Control and Inspection in American Law. After five years as professor of law at the University of Pennsylvania, he became a member of the Columbia Law School faculty in 1962. Simultaneously, Professor Henkin was also a faculty member of the School of International and Public Affairs, as well as of the Political Science Department in Columbia's Graduate School of the Arts and Sciences. He was the Hamilton Fish Professor of International Law and Diplomacy. Later, Professor Henkin was the Harlan Fiske Stone Professor of Constitutional Law, a position he held until he was designated University Professor in 1981.

Professor Henkin divided his time and interests among constitutional law, international law, law and diplomacy, and human rights, and specialized in the legal aspects of American foreign relations and international and comparative human rights.

He held the position of chairman of the board of directors for the Columbia University Center for the Study of Human Rights. In addition, Professor Henkin was the founding chair and director of the Law School's Institute of Human Rights. In 1982, the Law School awarded him the Medal for Excellence and, in 1999, it honored him by establishing the Louis Henkin Professorship in Human and Constitutional Rights.

Professor Henkin held positions in numerous domestic and international governing bodies. He served as a U.S. member of the Permanent Court of Arbitration from 1963-1969, as well as a member of the Advisory Committee on International Law at the U.S. Department of State from 1967-69, 1975-80, 1993-2010. In addition, he was an adviser on the Law of the Sea from 1973-80; president of the American Society of International Law from 1992-94; co-editor-in-chief of the American Journal of International Law from 1976-1984; chief reporter of the American Law Institute's Restatement of the Foreign Relations Law of the United States (Third); a fellow of the American Academy of Arts and Sciences; and on the board of directors of Human Rights First. Professor Henkin was a member of the Institut de Droit International, the American Philosophical Society, and the Human Rights Committee pursuant to International Covenant on Civil and Political Rights.

Professor Henkin earned a Silver Star for service in the U.S. Army during World War II.

He passed away on October 14, 2010.