Alasdair Chalmers MacIntyre (12 January 1929 – 21 May 2025) was a Scottish-American philosopher who contributed to moral and political philosophy as well as history of philosophy and theology. MacIntyre's After Virtue (1981) is one of the most important works of Anglophone moral and political philosophy in the 20th century. He was a senior research fellow at the Centre for Contemporary Aristotelian Studies in Ethics and Politics (CASEP) at London Metropolitan University, emeritus Professor of Philosophy at the University of Notre Dame, and permanent senior distinguished research fellow at the Notre Dame de Nicola Center for Ethics and Culture. During his lengthy academic career, he also taught at Brandeis University, Duke University, Vanderbilt University, and Boston University.

Alasdair Chalmers MacIntyre was born on 12 January 1929 in Glasgow, to Eneas and Greta (Chalmers) MacIntyre. He was educated at Queen Mary College, London, and had a Master of Arts degree from the University of Manchester, where his philosophy teacher was Dorothy Emmet and his fellow student was Herbert McCabe and from the University of Oxford. He began his teaching career in 1951 at Manchester. He married Ann Peri, with whom he had two daughters, Jean and Toni. He taught at the University of Leeds, the University of Essex and the University of Oxford in the United Kingdom, before moving to the US in around 1969. MacIntyre was something of an intellectual nomad, having taught at many universities in the US. He had held the following positions:

He had also been a visiting professor at Princeton University and was president of the American Philosophical Association. In 2010, he was awarded the Aquinas Medal by the American Catholic Philosophical Association. He was a member of the American Academy of Arts and Sciences (elected 1985), the British Academy (1994), the Royal Irish Academy (1999), and the American Philosophical Society (2005).

From 2000, he was the Rev. John A. O'Brien Senior Research Professor in the Department of Philosophy (emeritus since 2010) at the University of Notre Dame, Indiana, US. He was also professor emerit and emeritus at Duke University. In July 2010, he became senior research fellow at London Metropolitan University's Centre for Contemporary Aristotelian Studies in Ethics and Politics. After his retirement from active teaching in 2010, MacIntyre remained the senior distinguished research fellow of the Notre Dame de Nicola Center for Ethics and Culture, where he retained an office. He continued to make public presentations, including an annual keynote as part of the de Nicola Center for Ethics and Culture's Fall Conference.

MacIntyre was married three times. From 1953 to 1963, he was married to Ann Peri, with whom he had two daughters. From 1963 to 1977, he was married to former teacher and now poet Susan Willans, with whom he had a son and daughter. From 1977 to his death, he was married to philosopher Lynn Joy, who is also on the philosophy faculty at Notre Dame.

MacIntyre died on 21 May 2025 at a care facility in South Bend, Indiana, at the age of 96.

MacIntyre's approach to moral philosophy interweaves a number of complex strands. Although he largely aims to revive an Aristotelian moral philosophy based on the virtues, he claims a "peculiarly modern understanding" of this task.

This "peculiarly modern understanding" largely concerns MacIntyre's approach to moral disputes. Unlike some analytic philosophers who try to generate moral consensus on the basis of rationality, MacIntyre uses the historical development of ethics to circumvent the modern problem of "incommensurable" moral notions, whose merits cannot be compared in any common framework. Following Hegel and Collingwood, he offers a "philosophical history" (as opposed to analytical and phenomenological approaches) in which he concedes from the beginning that "there are no neutral standards available by appeal to which any rational agent whatsoever could determine" the conclusions of moral philosophy.