Swiss Catholic theologian, priest, and the most publicly visible reformist voice within post-conciliar Catholicism; author of the Infallible? (1970) critique that led in 1979 to the Vatican's withdrawal of his missio canonica — his license to teach as a Catholic theologian — and, in his later decades, founder of the Global Ethic project, the principal theological vehicle for interfaith moral dialogue in the late twentieth and early twenty-first century.
Küng was born in Sursee in the Swiss canton of Lucerne, studied philosophy and theology at the Pontifical Gregorian University in Rome, was ordained in 1954, and took his doctorate at the Institut Catholique de Paris with a dissertation on Karl Barth's doctrine of justification that argued — against the received Catholic/Protestant division — that Barth's position and the Council of Trent's were reconcilable. The book, Justification (1957), was the basis of his reputation: Barth himself provided a foreword endorsing its central claim. In 1960 he was appointed to the chair of Fundamental Theology at the University of Tübingen, where his colleague and sometime ally was Joseph Ratzinger, the future Benedict XVI. Both were appointed as periti, expert theological advisors, to the Second Vatican Council (1962–65) under John XXIII; Küng's book The Council, Reform and Reunion (1961) was one of the texts that helped shape the reformist agenda of the Council.
The divergence from Ratzinger opened in the late 1960s and became the decisive fact of Küng's career. The Church (1967) argued for a collegial rather than hierarchical ecclesiology; Infallible? An Inquiry (1970) argued that the 1870 dogma of papal infallibility had neither scriptural nor patristic warrant and was a doctrinal mistake. The book sold widely, drew the response of the Congregation for the Doctrine of the Faith, and after a nine-year internal process, on 18 December 1979, the Vatican issued a Declaration withdrawing Küng's missio canonica. He retained his priesthood and his chair at Tübingen (the university moved him to a non-faculty-of-Catholic-theology institute it created for him, the Institute for Ecumenical Research, which he directed until 1996), but could no longer teach as a Catholic theologian. The case was the most widely publicized instance of post-conciliar Vatican discipline and the moment at which the liberal and conservative wings of post-Vatican II Catholicism visibly parted.
The middle work is a large, systematic Christian apologetics addressed to secular modernity: On Being a Christian (1974), Does God Exist? (1978), Eternal Life? (1982). The late turn, from the mid-1980s onward, is toward interreligious and interethical work. Christianity and the World Religions (with scholars of Islam, Hinduism, and Buddhism, 1984) and Global Responsibility: In Search of a New World Ethic (1990) argue that the late-modern world requires a minimal shared ethic drawn from the common moral core of the world's religions. The Declaration Toward a Global Ethic, drafted by Küng, was adopted by the 1993 Parliament of the World's Religions in Chicago. The Project Weltethos, which he directed from Tübingen, remains the principal institutional vehicle for that program.
Küng was the author of more than thirty books, a public interlocutor of Benedict XVI (the two met at Castel Gandolfo in 2005 in a cautious reconciliation), and, at the end, an advocate — in A Dignified Dying (2009) — for the legalization of assisted dying, on which he gave his own reasons in his final years of Parkinson's disease. He died in Tübingen in 2021.