Japanese moral philosopher and historian of ideas, outstanding among modern Japanese thinkers who have tried to combine the Eastern moral spirit with Western ethical ideas.

Watsuji studied philosophy at Tokyo University and became professor of ethics at the universities of Kyōto (1931–34) and Tokyo (1934–49). His earliest writings include the two notable works A Study of Nietzsche (1913) and Søren Kierkegaard (1915), by which he paved the way for the introduction of Existentialism into Japan decades later. Then he turned to the study of the spirit of ancient Japanese culture and of Japanese Buddhism, writing books and essays treating various aspects of Japanese culture. He extended his research farther afield, into early Buddhism in India and its subsequent developments. His major writings, however, belong in the field of ethics: (ethics) Ethics as a Philosophy of Man (1934), Ethics, 3 vol. (1937–49), and History of Ethical Thought in Japan, 2 vol. (1952).

Watsuji tried to create a systematic Japanese ethics using Western categories. In contrast to what he saw as Western ethics' overemphasis on the private individual, Watsuji emphasized man both as an individual and as a social being who is deeply involved with his society. Watsuji introduced certain Buddhist dialectic elements in order to show how the individual is absorbed into society, and he cited various aspects of Japanese art and culture as expressing the interdependence of man and society. He developed his view of life as it applies to mutual personal and social relations, from the simplest to the fully integrated—from the family to the state.

Only one of Watsuji's works is available in English translation: A Climate: A Philosophical Study, translated by Geoffrey Bownas (1961, reprinted as Climate and Culture, 1988).