Sartre was a leading figure of the 20th-century movement called existentialism, and through works such as the novel 'Nausea' and the play 'No Exit' he argued that each person creates his or her own existence by acting. He stated that freedom is inescapable and that we are always forced to choose, a burden he called existential anxiety. Drawing on his experience in the French Resistance during World War II, he regarded literature as a tool for social engagement and spoke out on political issues. His fusion of thought and practice strongly influenced young people, fueling protest movements against the Vietnam War and inspiring the student uprisings of 1968. Although the Nobel Prize honored these achievements, Sartre declined it, saying that a writer should keep distance from institutions, thus turning his philosophy into deed.

Building on Husserlian phenomenology and influenced by Heidegger, Sartre developed an existentialism centered on subjectivity and freedom. In his magnum opus 'Being and Nothingness' he analyzes the split between being-in-itself and being-for-itself, arguing that humans ceaselessly project themselves and give meaning to the world. Through the notion of 'bad faith' he criticizes the self-deception in which people hide behind social roles to avoid the weight of freedom. His novels and plays translate these abstract debates into human drama; politically charged works such as 'The Wall' or 'The Flies' call intellectuals to social responsibility. From the 1950s onward he entered into dialogue with Marxism, endorsed anti-colonial struggles, and attempted a synthesis of philosophy and political theory in 'Critique of Dialectical Reason.' This multifaceted activity motivated the Literature Prize committee, while his insistence on autonomy from state and authority prompted him to decline the award.

In 'Being and Nothingness' Sartre redefines consciousness from a project-oriented perspective, positing the néant as an internal negation that configures the en-soi and thus constitutes worldhood. This move secularizes Kantian autonomy by grounding value not in a transcendent entity but in the subject’s projection. He further defends freedom against determinism through an anti-Freudian reading and links historicity to subjectivity via the concept of situation. 'Critique of Dialectical Reason' extends the theory of alienation to collective praxis, integrating structural constraints without diluting class struggle, though its unfinished state problematizes the allure of totalization itself. These theoretical innovations, combined with interventions in events such as the Algerian War, the Prague Spring, and May 1968, forged Sartre’s transdisciplinary authority, a breadth recognized by the Nobel committee.