Early years
Simone Lucie-Ernestine-Marie-Bertrand de Beauvoir was born on January 9, 1908 in Paris to Georges Bertrand and Françoise (Brasseur) de Beauvoir. The oldest of two daughters of a conventional family from the Parisian 'bourgeoisie', she depicts herself in the first volume of her autobiography (Memoirs of a Dutiful Daughter) as a girl with a strong commitment to the patriarchal values of her family, religion, and country.

From the outset, she is subject to the opposing influences of her agnostic father and her devoutly Catholic mother. The two formative peer-relationships of her childhood and adolescence involve her sister Hélène (whom she calls Poupette) and her friend Zaza. She traces back to her relationship with Poupette, whom she sought to teach and influence from an early age, her taste for teaching, and it is the tragic life and death of Zaza that forms the subject matter for her first, unsuccessful, literary endeavours.

Middle years
After passing the baccalauréat exams in mathematics and philosophy, she studied mathematics at the Institut Catholique and literature/languages at the Institut Sainte-Marie, then philosophy at the Sorbonne. While at the Sorbonne, she met Jean-Paul Sartre in 1929, who was taking courses there while enrolled at the elite École Normale Supérieure. It is a common misconception that de Beauvoir studied at the Ecole Normale. She was, however, well acquainted with the school and its curriculum, thanks to Sartre and others within their philosophic circle.

In 1929, de Beauvoir also became the youngest person ever to obtain the aggrégation in philosophy. Sartre was first that year, but she was a close second. While at the Sorbonne, she acquired her lifelong nickname, Castor (the French word for "beaver")—a pun derived from the resemblance of her surname to "beaver".

In 1943, de Beauvoir published L'Invitée (She Came to Stay, 1943), a fictionalized chronicle of her lesbian relationship with Olga Kosakiewicz, one of her students in the Rouen secondary school where she taught during the early 30s. The novel also delves into the complex relationship between de Beauvoir and Sartre, as well as how that relationship was affected by the menage a trois with Kosakiewicz.

Later years
At the end of World War II, de Beauvoir and Sartre edited Les Temps Modernes, a political journal Sartre founded along with Maurice Merleau-Ponty and others. De Beauvoir used Les Temps Modernes to promote her own work and remained an editor until her death.

Although her book Pour Une Morale de L'ambiguïté (The Ethics of Ambiguity, 1947) has been little noticed, it is perhaps the most accessible point of entry into French existentialism. Its simplicity keeps it understandable, in contrast to the gnashing of teeth that many experience when reading Sartre's highly analytical Being and Nothingness. The ambiguity about which de Beauvior writes clears up some inconsistencies many, Sartre included, have found in major existential works such as Being and Nothingness.

De Beauvoir was uninhibitedly bisexual. But when (the late 1940s) she wrote The Second Sex, she had never experienced heterosexual orgasm. Immediately after delivering the manuscript to her publisher, she left for an extended visit to the USA, having been invited by Nelson Algren whom she had met during a 1947 visit to the USA, when she also met Richard Wright.

In the hands of Algren and of other American men to whom he introduced her, in sweltering Chicago, de Beauvoir finally experienced orgasm with men. Thus in her own way, de Beauvoir anticipated the later raunchy feminism of Erica Jong and Germaine Greer. Algren, no paragon of primness himself, was outraged by the frank way de Beauvoir later described her American sexual experiences in Les Mandarins (dedicated to Algren and on whose character Lewis Brogan is based) and elsewhere, venting his outrage when reviewing American translations of her work. Much bearing on this episode in de Beauvoir's life, including her love letters to Algren, entered the public domain only after her death. On De Beauvoir's sexuality and the paper trail she left.

The Second Sex
De Beauvoir's The Second Sex, published in French in 1949, sets out a feminist existentialism with a significant Freudian aspect. As an existentialist, de Beauvoir accepts the precept that existence precedes essence; hence one is not born a woman, but becomes one. Her analysis focuses on the concept of The Other. It is the (social) construction of Woman as the quintessential Other that de Beauvoir identifies as fundamental to women's oppression.

De Beauvoir argues that women have historically been considered deviant, abnormal. She submits that even Mary Wollstonecraft considered men to be the ideal toward which women should aspire. De Beauvoir says that this attitude has limited women's success by maintaining the perception that they are a deviation from the normal, and are outsiders attempting to emulate "normality". For feminism to move forward, this assumption must be set aside.

De Beauvoir asserted that women are as capable of choice as men, and thus can choose to elevate themselves, reducing male consciousness to immanence. An example of women choosing transcendence, one not found in de Beauvoir's writings, would be a sorority in which women could perceive their collective as a normal female "we," reducing male consciousness to the Other.

Death and afterwards
Her 1970 The Coming of Age is a very rare instance of an intellectual meditation on the decline and solitude all humans experience if they do not die before about age 60. In 1981 she wrote La Cérémonie Des Adieux (A Farewell to Sartre), a painful account of Sartre's last years. She is buried next to him at the Cimetière du Montparnasse in Paris. Since her death, her reputation has grown, not only because she is seen as the mother of post-1968 feminism, especially in academia, but also because of a growing awareness of her as a major French thinker, existentialist and otherwise. She is seen as having influenced Sartre's masterpiece, Being and Nothingness, while also having written much on philosophy that is independent of Sartrian existentialism.