Cornelius Castoriadis (named after Saint Cornelius the Centurion) was born on 11 March 1922 in Constantinople, the son of Kaisar (“Caesar”) and Sophia Kastoriadis. His family had to move in July 1922 to Athens due to the Greek–Turkish population exchange. He developed an interest in politics after he came into contact with Marxist thought and philosophy at the age of 13. At the same time he began studying traditional philosophy after purchasing a copy of the book History of Philosophy (Ιστορία της Φιλοσοφίας, 1933, 2 vols.) by the historian of ideas Nikolaos Louvaris [el].

Sometime between 1932 and 1935, Maximiani Portas (later known as “Savitri Devi”) was the French tutor of Castoriadis. During the same period, he attended the 8th Gymnasium of Athens in Kato Patisia, from which he graduated in 1937.

His first active involvement in politics occurred during the Metaxas Regime (1937), when he joined the Athenian Communist Youth (Κομμουνιστική Νεολαία Αθήνας, Kommounistiki Neolaia Athinas), a section of the Young Communist League of Greece. In 1941 he joined the Communist Party of Greece (KKE), only to leave one year later in order to become an active Trotskyist. The latter action resulted in his persecution by both the Germans and the Communist Party.

In 1944 he wrote his first essays on social science and Max Weber, which he published in a magazine named Archive of Sociology and Ethics (Αρχείον Κοινωνιολογίας και Ηθικής, Archeion Koinoniologias kai Ithikis). Castoriadis heavily criticized the actions of the KKE during the December 1944 clashes between the communist-led ELAS on one side, and the Papandreou government aided by British troops on the other.

In December 1945, three years after earning a bachelor’s degree in law, economics and political science from the School of Law, Economics and Political Sciences of the University of Athens (where he met and collaborated with the Neo-Kantian intellectuals Konstantinos Despotopoulos, Panagiotis Kanellopoulos, Konstantinos Tsatsos), he got aboard the RMS Mataroa, a New Zealand ocean liner, to go to Paris (where he remained permanently) to continue his studies under a scholarship offered by the French Institute of Athens. The same voyage—organized by Octave Merlier—also brought from Greece to France a number of other Greek writers, artists and intellectuals, including Constantine Andreou, Kostas Axelos, Georges Candilis, Costa Coulentianos, Emmanuel Kriaras, Adonis A. Kyrou, Kostas Papaïoannou, and Virgile Solomonidis.

Once in Paris, Castoriadis joined the Trotskyist Parti Communiste Internationaliste (PCI). He and Claude Lefort constituted a Chaulieu–Montal Tendency in the French PCI in 1946. In 1948, they experienced their “final disenchantment with Trotskyism”, leading them to break away to found the libertarian socialist and councilist group and journal Socialisme ou Barbarie (S. ou B., 1949–1966), which included Jean-François Lyotard and Guy Debord as members for a while, and profoundly influenced the French intellectual left. Castoriadis had links with the group known as the Johnson–Forest Tendency until 1958. Also strongly influenced by Castoriadis and Socialisme ou Barbarie were the British group and journal Solidarity and Maurice Brinton.

In his 1949 essay “The Relations of Production in Russia”, Castoriadis developed a critique of the supposed socialist character of the government of the Soviet Union. According to Castoriadis, the central claim of the Stalinist regime at the time was that the mode of production in Russia was socialist, but the mode of distribution was not yet a socialist one since the socialist edification in the country had not yet been completed. However, according to Castoriadis’ analysis, since the mode of distribution of the social product is inseparable from the mode of production, the claim that one can have control over distribution while not having control over production is meaningless.

In the latter years of Socialisme ou Barbarie, Castoriadis came to reject the Marxist theories of economics and of history, especially in an essay on “Modern Capitalism and Revolution”, first published in Socialisme ou Barbarie in 1960–61 (first English translation in 1963 by Solidarity). Castoriadis’ final Socialisme ou Barbarie essay was “Marxism and Revolutionary Theory”, published in April 1964 – June 1965. There he concluded that a revolutionary Marxist must choose either to remain Marxist or to remain revolutionary.

When Jacques Lacan’s disputes with the International Psychoanalytical Association led to a split and the formation of the École Freudienne de Paris (EFP) in 1964, Castoriadis became a member (as a non-practitioner).

In 1967, Castoriadis submitted a proposal for a doctoral dissertation on the philosophy of history to Paul Ricœur (then at the University of Nanterre). An epistolary dialogue began between them but Ricœur’s obligations to the University of Chicago in the 1970s were such that their collaboration was not feasible at the time. The subject of his thesis would be Le fondement imaginaire du social-historique (The Imaginary Foundations of the Social-Historical) (see below).

In 1968 Castoriadis married Piera Aulagnier, a French psychoanalyst who had undergone psychoanalytic treatment under Jacques Lacan from 1955 until 1961.

In 1969 Castoriadis and Aulagnier split from the EFP to join the Organisation psychanalytique de langue française (O.P.L.F.), the so-called “Quatrième Groupe”, a psychoanalytic group that claims to follow principles and methods that have opened up a third way between Lacanianism and the standards of the International Psychoanalytical Association.

Castoriadis began to practice analysis in 1973 (he had undergone analysis in the 1960s first with Irène Roubleff and then later with Michel Renard).

In his 1975 work, L’Institution imaginaire de la société (Imaginary Institution of Society), and in Les carrefours du labyrinthe (Crossroads in the Labyrinth), published in 1978, Castoriadis began to develop his distinctive understanding of historical change as the emergence of irrecoverable otherness that must always be socially instituted and named in order to be recognized. Otherness emerges in part from the activity of the psyche itself. Creating external social institutions that give stable form to what Castoriadis terms the (ontological) “magma of social significations” allows the psyche to create stable figures for the self, and to ignore the constant emergence of mental indeterminacy and alterity.

In his 1980 Facing the War text, he took the view that Russia had become the primary world military power. To sustain this, in the context of the visible economic inferiority of the Soviet Union in the civilian sector, he proposed that the society may no longer be dominated by the one-party state bureaucracy but by a “stratocracy”—a separate and dominant military sector with expansionist designs on the world. He further argued that this meant there was no internal class dynamic which could lead to social revolution within Russian society and that change could only occur through foreign intervention.

In 1980, he joined the faculty of the École des Hautes Études en Sciences Sociales (EHESS) as Directeur d’études (Director of Studies). He had been elected Directeur de recherche (Director of Research) in EHESS at the end of 1979 after submitting his previously published material in conjunction with a defense of his intellectual project of connecting the disciplines of history, sociology and economy through the concept of the social imaginary (see below). His teaching career at the EHESS lasted sixteen years.

In 1980, he was also awarded his State doctorate from the University of Nanterre; the final title of his thesis under Ricœur (see above) was L’Élément imaginaire de l’histoire (The Imaginary Element in History).

In 1989, he was awarded an Honorary Doctorate in Social Sciences by Panteion University and in 1993 another one in Education Sciences by the Democritus University of Thrace.

In 1992, he joined the libertarian socialist journal Society and Nature (established by Takis Fotopoulos) as a writer; the magazine also featured such writers as Murray Bookchin and Noam Chomsky.

He died on 26 December 1997 from complications following heart surgery. He was survived by Zoe Christofidi (his wife at the time of his death), his daughter Sparta (by an earlier relationship with Jeanine “Rilka” Walter, “Comrade Victorine” in the Fourth International), and Kyveli, a younger daughter from his marriage with Zoe.