Simone de Beauvoir was born in Paris, the eldest daughter of Georges Bertrand de Beauvoir, a legal secretary who once aspired to be an actor, and Françoise (born) Brasseur, a wealthy banker’s daughter and devout Catholic. Her younger sister, Hélène, was born two years later. The family struggled to maintain their bourgeois status after losing much of their fortune shortly after World War I, and Françoise insisted that the two daughters be sent to a prestigious convent school. Beauvoir herself was deeply religious as a child — at one point intending to become a nun — until a crisis of faith at age 14. She remained an atheist for the rest of her life.

Beauvoir was intellectually precocious, fueled by her father’s encouragement: he reportedly would boast, “Simone thinks like a man!” After passing baccalaureate exams in mathematics and philosophy in 1925, she studied mathematics at the Institut Catholique and literature / languages at the Institut Sainte - Marie. She then studied philosophy at the Sorbonne, writing her thesis on Leibniz for Léon Brunschvicg. She first worked with Maurice Merleau - Ponty and Claude Lévi - Strauss when all three completed their practice teaching requirements at the same secondary school. Although not officially enrolled, she sat in on courses at the École Normale Supérieure in preparation for the agrégation in philosophy, a highly competitive postgraduate examination which serves as a national ranking of students. It was while studying for the agrégation that she met École Normale students Jean - Paul Sartre, Paul Nizan, and René Maheu (who gave her the lasting nickname "Castor", or beaver). The jury for the agrégation narrowly awarded Sartre first place instead of Beauvoir, who placed second and, at age 21, was the youngest person ever to pass the exam.

Sartre was dazzlingly intelligent and was just under 5 feet (1.5 m) tall. During October 1929, the two became a couple and Sartre asked her to marry him. One day while they were sitting on a bench outside the Louvre, he said, "Let's sign a two - year lease". Near the end of her life, Beauvoir said, "Marriage was impossible. I had no dowry." So they became an imaginary married couple. Beauvoir chose to never marry and did not set up a joint household with Sartre. She never had children. This gave her time to earn an advanced academic degree, to join political causes and to travel, write, teach, and to have (both male and female – the latter often shared) lovers.

She started her teaching career at a secondary school in Marseilles in 1931 and moved to the Lycée Pierre Corneille in Rouen.

A number of de Beauvoir's young female lovers were underage, and the nature of some of these relationships, some of which she instigated while working as a school teacher, has led to a biographical controversy and debate over whether de Beauvoir had inclinations towards ephebophilia. A former student, Bianca Lamblin, originally Bianca Bienenfeld, later wrote critically about her seduction by her teacher, Simone de Beauvoir, when she was a 17 year old lycee student in her book, Mémoires d'une jeune fille rangée. In 1943, de Beauvoir was suspended from her teaching job, due to an accusation that she had, in 1939, seduced her 17 year old lycee pupil Nathalie Sorokine. De Beauvoir would, along with other French intellectuals, later petition for an abolition of all age of consent laws in France.

Beauvoir published new first novel She Came to Stay in 1943. It is a fictionalized chronicle of her and Sartre's sexual relationship with Olga Kosakiewicz and Wanda Kosakiewicz. Olga was one of her students in the Rouen secondary school where Beauvoir taught during the early 30s. She grew fond of Olga. Sartre tried to pursue Olga but she denied him; he began a relationship with her sister Wanda instead. Sartre supported Olga for years until she met and married her husband, Beauvoir's lover Jacques - Laurent Bost. At Sartre's death, he was still supporting Wanda. In the novel, set just before the outbreak of World War II, Beauvoir makes one character from the complex relationships of Olga and Wanda. The fictionalized versions of Beauvoir and Sartre have a ménage à trois with the young woman. The novel also delves into Beauvoir and Sartre's complex relationship and how it was affected by the ménage à trois.

Beauvoir's metaphysical novel She Came to Stay was followed by many others, including The Blood of Others which explores the nature of individual responsibility.

In 1944 Beauvoir wrote her first philosophical essay, Pyrrhus et Cinéas, a discussion of a existentialist ethics.

Her second essay, The Ethics of Ambiguity, (1947) is perhaps the most accessible entry into French existentialism. Its simplicity keeps it understandable, in contrast to the abstruse character of Sartre's Being and Nothingness. In the essay Beauvoir clears up some inconsistencies that many, Sartre included, have found in major existentialist works such as Being and Nothingness.

At the end of World War II, Beauvoir and Sartre edited Les Temps Modernes, a political journal Sartre founded along with Maurice Merleau - Ponty and others. Beauvoir used Les Temps Modernes to promote her own work and explore her ideas on a small scale before fashioning essays and books. Beauvoir remained an editor until her death.

Chapters of Le deuxième sexe (The Second Sex) were originally published in Les Temps modernes, in June 1949. The second volume came a few months after the first in France. It was very quickly published in America as The Second Sex, due to the quick translation by Howard Parshley, as prompted by Blanche Knopf, wife of publisher Alfred A. Knopf. Because Parshley had only a basic familiarity with the French language, and a minimal understanding of philosophy (he was a professor of biology at Smith College), much of Beauvoir's book was mistranslated or inappropriately cut, distorting her intended message. For years Knopf prevented the introduction of a more accurate retranslation of Beauvoir's work, declining all proposals despite the efforts of existentialist scholars. Only in 2009 was there a second translation, to mark the 60th anniversary of the original publication. Constance Borde and Sheila Malovany - Chevallier produced the first integral translation, reinstating a third of the original work.

Beauvoir anticipated the sexually charged feminism of Erica Jong and Germaine Greer.

In the chapter "Woman: Myth and Reality" of The Second Sex, Beauvoir argued that men had made women the "Other" in society by putting a false aura of "mystery" around them. She argued that men used this as an excuse not to understand women or their problems and not to help them, and that this stereotyping was always done in societies by the group higher in the hierarchy to the group lower in the hierarchy. She wrote that this also happened on the basis of other categories of identity, such as race, class, and religion. But she said that it was nowhere more true than with sex in which men stereotyped women and used it as an excuse to organize society into a patriarchy.

The Second Sex, published in French, sets out a feminist existentialism which prescribes a moral revolution. As an existentialist, Beauvoir believed that existence precedes essence; hence one is not born a woman, but becomes one. Her analysis focuses on the Hegelian concept of the Other. It is the (social) construction of Woman as the quintessential Other that Beauvoir identifies as fundamental to women's oppression. The capitalized 'O' in "other" indicates the wholly other.

Beauvoir argued that women have historically been considered deviant, abnormal. She said that even Mary Wollstonecraft considered men to be the ideal toward which women should aspire. Beauvoir said that this attitude limited women's success by maintaining the perception that they were a deviation from the normal, and were always outsiders attempting to emulate "normality". She believed that for feminism to move forward, this assumption must be set aside.

Beauvoir asserted that women are as capable of choice as men, and thus can choose to elevate themselves, moving beyond the 'immanence' to which they were previously resigned and reaching 'transcendence', a position in which one takes responsibility for oneself and the world, where one chooses one's freedom.

A new translation of The Second Sex for the first time gives access to the entire text in English, as Irene Gammel writes in a Globe and Mail review: "The single most important advantage of this new translation is its completeness, combined with the translators' courage to transpose Beauvoir's existential language, thereby giving readers a sense of Beauvoir's channeling of Hegel, Marx and others."

Published in 1954 The Mandarins is set just after the end of World War II and won her France's highest literary prize, the Prix Goncourt. The book follows the personal lives of philosophers and friends among Sartre and Beauvoir's intimate circle including her relationship with American writer Nelson Algren, to whom the book was dedicated. Algren was outraged by the frank way Beauvoir described their sexual experiences in both The Mandarins and her autobiographies. He vented his outrage when reviewing American translations of her work. Much material bearing on this episode in Beauvoir's life, including her love letters to Algren, entered the public domain only after her death.

Beauvoir wrote popular travel diaries about her travels in the United States and China, and published essays and fiction rigorously, especially throughout the 1950s and 1960s. She published several volumes of short stories, including The Woman Destroyed, which, like some of her other later work, deals with aging.

In 1980 she published When Things of the Spirit Come First, a set of short stories centered around and based upon women important to her earlier years. The stories were written long before the novel She Came to Stay, but Beauvoir did not think they were worthy of publication until about forty years later.

Sartre and Merleau - Ponty had a longstanding feud, which led Merleau - Ponty to leave Les Temps Modernes. Beauvoir sided with Sartre and ceased to associate with Merleau - Ponty. In Beauvoir's later years, she hosted the journal's editorial meetings in her flat and contributed more than Sartre, whom she often had to force to offer his opinions.

Beauvoir also notably wrote a four volume autobiography, consisting of: Memoirs of a Dutiful Daughter; The Prime of Life; Force of Circumstance (sometimes published in two volumes in English translation: After the War and Hard Times); and All Said and Done.

In the 1970s Beauvoir became active in France's women's liberation movement. She signed the Manifesto of the 343 in 1971, a list of famous women who claimed to have had an abortion, then illegal in France. Some argue most of the women had not had abortions, including Beauvoir, but given the secrecy surrounding the issue, this cannot be known. Signatories were diverse as Catherine Deneuve, Delphine Seyrig and Beauvoir's sister Poupette. In 1974, abortion was legalized in France.

Her 1970 long essay La Vieillesse (The Coming of Age) is a rare instance of an intellectual meditation on the decline and solitude all humans experience if they do not die before about age 60.

In about 1976 Beauvoir and Sylvie Le Bon made a trip to New York in the USA to visit Kate Millett on her farm. A film was made of their conversation.

In 1981 she wrote La Cérémonie Des Adieux (A Farewell to Sartre), a painful account of Sartre's last years. In the opening of Adieux, Beauvoir notes that it is the only major published work of hers which Sartre did not read before its publication. She and Sartre always read one another's work.

After Sartre died, Beauvoir published his letters to her with edits to spare the feelings of people in their circle who were still living. After Beauvoir's death, Sartre's adopted daughter and literary heir Arlette Elkaïm would not let many of Sartre's letters be published in unedited form. Most of Sartre's letters available today have Beauvoir's edits, which include a few omissions but mostly the use of pseudonyms. Beauvoir's adopted daughter and literary heir Sylvie Le Bon, unlike Elkaïm, published Beauvoir's unedited letters to both Sartre and Algren.

Beauvoir died of pneumonia in Paris, aged 78. She is buried next to Sartre at the Cimetière du Montparnasse in Paris.

Since her death, her reputation has grown. Especially in academia, she is considered the mother of post 1968 feminism. There has also been a growing awareness of her as a major French thinker and existentialist philosopher.

Contemporary discussion analyzes the influences of Beauvoir and Sartre on one another. She is seen as having influenced Sartre's masterpiece, Being and Nothingness, while also having written much on philosophy that is independent of Sartrean existentialism. Some scholars have explored the influences of her earlier philosophical essays and treatises upon Sartre's later thought. She is studied by many respected academics both within and outside philosophy circles, including Margaret A. Simons and Sally Scholtz. Beauvoir's life has also inspired numerous biographies.

In 2006, the city of Paris commissioned architect Dietmar Feichtinger to design a sophisticated footbridge across the Seine River. The bridge was named the Passerelle Simone - de - Beauvoir in her honor. It leads to the new Bibliothèque nationale de France.