In September 1999, Father John Langan, S.J., was named to be the Joseph Cardinal Bernardin Professor of Catholic Social Thought at Georgetown University. He is a senior research scholar in the Kennedy Institute, where from 1987 to 1999 he served as Rose Kennedy Professor of Christian Ethics, and a professor in the philosophy department as well as a member of the core faculty of the School of Foreign Service at Georgetown. He teaches courses on ethical theory, on ethics and international affairs, human rights, just war theory, and capitalism and morality. He has also taught at Loyola University of Chicago, Drew University, and Yale Divinity School. He holds a Ph.D. in philosophy from the University of Michigan. He earned bachelor's and master's degrees in classics from Loyola University of Chicago and a bachelor of divinity degree from Woodstock College. He entered the Society of Jesus in 1957 and was ordained to the priesthood in Detroit in 1972. From 1975 to 1995 he was a fellow of the Woodstock Theological Center in Washington DC. He has served regularly as a visiting priest in the parish of St. Thomas a Becket, Reston, Virginia, since 1983.

He has edited or co-edited six books, among which are Human Rights in the Americas: The Struggle for Consensus (1982), The Nuclear Dilemma and the Just War Tradition (1986), The American Search for Peace: Moral Reasoning, National Security, and Religious Hope (1991) and Catholic Universities in Church and Society (1993). He has recently edited A Moral Vision for America, a collection of the addresses of Joseph Cardinal Bernardin on ethics and public life in the United States. He has contributed articles to numerous collections of essays on religious and ethical aspects of social and political life as well as articles in such reference works as The New Dictionary of Catholic Social Thought, The New Dictionary of Theology, The Westminster Dictionary of Christian Ethics,and The Encyclopedia of Catholicism. His writing has appeared in a wide range of journals including Harvard Theological Review, Journal of Religious Ethics, Heythrop Journal. Etudes (Paris), Lumen Vitae (Brussels), Washington Quarterly, Orbis, Naval War College Review, Fordham Law Review, Commonweal, Christian Century, America, and The Tablet (London) as well as in the Washington Post and the Baltimore Sun. He is currently working on ethical questions about the war on terrorism and the war with Iraq and on a study of the ethics of military intervention for humanitarian purposes. He is also writing on the sexual abuse crisis in the Catholic Church.

He serves on the board of directors of Catholic Health Services of Long Island; Roper St. Francis (a health care system in Charleston SC); and the Carnegie Council on Ethics and International Affairs. He is currently chair of the board of Theological Studies, Inc., and in 2002 he served as president of the Jesuit Philosophical Association. He has served on the boards of the National Capital Presbytery Health Services and of the Bon Secours Health System (MD).

In January 2003 he was elected vice-president of the Society of Christian Ethics and will serve as president in 2004. The SCE is the main academic organization for scholars of religious ethics.