After completing his secondary education in Oran, Alg., Saint Laurent left for Paris to pursue a career in designing theatrical costumes and women's fashions. He attended fashion school for a short time and won first prize in an international design contest. When a Vogue magazine executive showed Christian Dior (Dior, Christian) some of Saint Laurent's sketches, he was hired immediately as Dior's assistant. He was 17 at the time.

As Dior's protégé, Saint Laurent was named the head of the House of Dior at Dior's death in 1957. Following the “little-girl” look and the A-line silhouette, he introduced more sophisticated, longer skirts and, in 1959, drastically shortened skirts. In 1960 he introduced the chic beatnik look of turtlenecks and black leather jackets edged with fur.

After induction into the French army in 1960, Saint Laurent suffered a nervous collapse and was replaced at the House of Dior by designer Marc Bohan. In 1962 Saint Laurent opened his own fashion house and quickly emerged as one of the most influential designers in Paris. He popularized trousers for women for both city and country wear. Metallic and transparent fabrics were prominent in his late '60s collections; in the 1970s, inspired by ethnic costume, he introduced the haute peasant look. During the 1960s and '70s his enterprises expanded to include ready-to-wear licenses, accessories, household linens, fragrances (notably Y 【1964】, Rive Gauche 【1971】, and Opium 【1977】), and men's clothes in addition to his couture business.

In 1983 the Metropolitan Museum of Art in New York held a retrospective of Saint Laurent's designs. He sold the ready-to-wear business to Gucci for some $1 billion in 1999 and shut down the couture house when he retired in 2002. In 2007 Saint Laurent was made a grand officer of the Legion of Honour.