After graduating with his Baccalauréat in 1943, he returned to Paris to enroll at the Sorbonne, where he was a student of the philosopher Gaston Bachelard.

It was during this time that he became acquainted with the works of Karl Marx, and the Vietnamese Marxist philosopher and phenomenologist Tran Duc Thao.

Finding further inspiration in Jean-Paul Sartre's L'Imaginaire, Châtelet entered a period of what he referred to as "Hegelo-Marxist Existentialism.

[5] Completing his thesis in 1959[7] Châtelet was awarded a Doctor of Letters in 1961, when his complimentary thesis, Logos et praxis: Recherches sur la signification théorique du marxisme (Logos and Praxis: Research on the Theoretical Significance of Marxism) was published by Les Éditions de Minuit.

[4][5] From a young age, Châtelet was actively engaged in current affairs,[6] putting up posters and distributing leaflets – some of which had Trotskyist undertones – around the Lycées at which he studied.

"[2][9] Châtelet's philosophy links thought and action, engaging in a restless combat with his contemporaries.

He also taught in high schools and pre-university classes throughout his career,[10] and occasionally participated in the seminars of Gilles Deleuze, with whom he was close friends.

[10] In Une histoire de la raison (A History of Reason), he shows the role of philosophy in the constitution of modern Western rationality.