WASHINGTON, D.C. — Jesuit Father John P. Langan, who became a respected expert on the Catholic Church’s teaching on the just-war tradition and Christian ethics throughout nearly 40 years as a professor, died March 20 at age 79.

The longtime professor of philosophy and Christian ethics at Georgetown University often was the go-to person to offer insights as a speaker and panelist on how the moral and religious commitments of the Catholic community could be understood and lived in a pluralistic world.

Langan’s research and writing widely explored the just-war theory and its application to questions surrounding issues such as nuclear armaments, terrorism, the U.S.-led war in Iraq, and the Syrian civil war. He also studied business ethics, human rights theory, capital punishment, Catholic social teaching, the place of religion in liberal political thought, and the ethical theories of St. Thomas Aquinas and St. Augustine.

He wrote pieces for various journals, including Peacemaking, Theological Studies, The Thomist and contributed reflections to various books and publications. He also edited “Catholic Universities in Church and Society” and “A Moral Vision for America, a collection of the addresses of Cardinal Bernardin on public policy and the consistent ethic of life.”

Langan was born in Hartford, Connecticut, Aug. 10, 1940. He entered the Jesuit Novitiate of St. Isaac Jogues in Wernersville, Pennsylvania, in 1957 after high school graduation in Detroit. He studied theology at Woodstock College in Maryland and holds a doctorate in philosophy from the University of Michigan.

Following ordination in 1972, Langan joined the staff of the newly formed Woodstock Theological Center in Maryland. He began teaching philosophy in 1981 at Georgetown and then at Yale Divinity School until 1986. He then returned to Woodstock as acting director and superior.

During the 1980s, Langan worked with the U.S. Conference of Catholic Bishops in drafting its statement against capital punishment and contributed to the bishops’ pastoral letters “The Challenge of Peace: God’s Promise and Our Response,” which addressed the nuclear arms race, and “Economic Justice for All” on the U.S. economy.

In 1987, Langan joined the Georgetown University faculty, becoming a professor of philosophy and Christian ethics. He later was named the Joseph Cardinal Bernardin professor of Catholic social thought at the school. In addition, he taught philosophy at Loyola University Chicago for two years and was rector of the Georgetown Jesuit community for five years.

Beyond his academic work, Langan served as a consultant to the Chemical Bank in New York and to the U.S. Navy Chaplains Corps. He served on the boards of Bon Secours Health System, Catholic Health Service of Long Island, Georgetown University Hospital, Society of Christian Ethics, Theological Studies and Georgetown University Press, where he was chairman. He also chaired the American section of the Council of Christian Approaches to Defense and Disarmament at King’s College in London.

In 2017, Langan moved to the Colombiere Jesuit Community in Baltimore where he continued to write and pray.

A private funeral service was held March 26 followed by burial at the Georgetown Jesuit Cemetery in Washington.