Nagel was born in Belgrade, Yugoslavia (now Serbia), to German Jewish refugees Carolyn (Baer) and Walter Nagel. Nagel arrived in the US in 1939, and was raised in, and around New York. He had no religious upbringing, but regards himself as a Jew.

Nagel married Doris Blum in 1954, divorcing in 1973. In 1979 he married Anne Hollander, who died in 2014.

Nagel received a BA in philosophy from Cornell University in 1958, where he was a member of the Telluride House and where he was introduced to the philosophy of Ludwig Wittgenstein. He then attended the University of Oxford on a Fulbright Scholarship and received a BPhil in 1960; while there, he studied with J. L. Austin, and H. Paul Grice. He received his PhD in philosophy from Harvard University in 1963. At Harvard, Nagel studied under John Rawls, whom Nagel later called “the most important political philosopher of the twentieth century.”

Nagel has been highly influential in the related fields of moral and political philosophy. Supervised by John Rawls, Nagel has been a long-standing proponent of a Kantian and rationalist approach to moral philosophy. His distinctive ideas were first presented in the short monograph The Possibility of Altruism, published in 1970. That book seeks by reflection on the nature of practical reasoning to uncover the formal principles that underlie reason in practice and the related general beliefs about the self that are necessary for those principles to be truly applicable to us. Nagel defends motivated desire theory about the motivation of moral action. According to motivated desire theory, when a person is motivated to moral action it is indeed true that such actions are motivated – like all intentional actions – by a belief and a desire. But it is important to get the justificatory relations right: when a person accepts a moral judgment he or she is necessarily motivated to act. But it is the reason that does the justificatory work of justifying both the action and the desire. Nagel contrasts this view with a rival view which believes that a moral agent can only accept that he or she has a reason to act if the desire to carry out the action has an independent justification. An account based on presupposing sympathy would be of this kind.

Nagel is probably most widely known within the field of philosophy of mind as an advocate of the idea that consciousness and subjective experience cannot, at least with the contemporary understanding of physicalism, be satisfactorily explained using the current concepts of physics. This position was primarily discussed by Nagel in one of his most famous articles: “What is it Like to Be a Bat?” (1974). The article’s title question, though often attributed to Nagel, was originally asked by Timothy L.S. Sprigge. The article was originally published in 1974 in The Philosophical Review, and has been reprinted several times, including in The Mind’s I (edited by Daniel Dennett and Douglas Hofstadter), Readings in the Philosophy of Psychology (edited by Ned Block), Nagel’s Mortal Questions (1979), The Nature of Mind (edited by David M. Rosenthal), and Philosophy of Mind: Classical and Contemporary Readings (edited by David J. Chalmers).

Nagel is a Fellow of the American Academy of Arts and Sciences and a Corresponding Fellow of the British Academy, and, in 2006, was elected as a member of the American Philosophical Society. He has held a fellowship from the Guggenheim Foundation, the National Science Foundation, and the National Endowment for the Humanities. In 2008, he was awarded a Rolf Schock Prize for his work in philosophy, the Balzan prize, and the honorary degree of Doctor of Letters from the University of Oxford.

Nagel has argued that ID should not be rejected as non-scientific, for instance writing in 2008 that “ID is very different from creation science,” and that the debate about ID “is clearly a scientific disagreement, not a disagreement between science and something else.” In 2009, he recommended Signature in the Cell by the philosopher and ID proponent Stephen C. Meyer in The Times Literary Supplement as one of his “Best Books of the Year.” Nagel does not accept Meyer’s conclusions but he endorsed Meyer’s approach, and argued in Mind and Cosmos that Meyer and other ID proponents, David Berlinski and Michael Behe, “do not deserve the scorn with which they are commonly met.”

In his 2012 book Mind and Cosmos, Nagel argues against a materialist view of the emergence of life and consciousness, writing that the standard neo-Darwinian view flies in the face of common sense. He writes that mind is a basic aspect of nature, and that any philosophy of nature that cannot account for it is fundamentally misguided. He argues that the principles that account for the emergence of life may be teleological, rather than materialist or mechanistic. Despite Nagel’s being an atheist and not a proponent of intelligent design (ID), his book was “praised by creationists”, according to the New York Times. Nagel writes in Mind and Cosmos that he disagrees with both ID defenders and their opponents, who argue that the only naturalistic alternative to ID is the current reductionist neo-Darwinian model.