On the evening of October 29, 1945, Jean-Paul Sartre delivered a much-anticipated lecture, advertised as “Existentialism is a Humanism,” to an overflow crowd in the Salle des Centraux on the Parisian Right Bank. As he was already well known for his novels Nausea and the recently published The Age of Reason and The Reprieve, his plays, The Flies and No Exit, and his philosophical essays, especially the daunting masterpiece Being and Nothingness, his talk was seen as the manifesto for this rapidly spreading style of thought. It is still the philosophical essay that people read when they seek an introduction to his work and to this movement in general. Yet it is the only piece that he openly regretted having published.
In what follows I shall survey the intellectual path that led Sartre to this juncture, the turn that it presaged, and the resultant works and deeds that came to define him as “Sartre.” This is a biography, the story of a life. But it is a philosophical biography, an account of the development of the thought and works of arguably the most famous philosopher of the twentieth century.