Born and raised in Oran, Algeria to French parents. His talent for design became evident as a teenager and at the tender age of 17, he left for Paris with the determination to work in a major fashion house. Soon after, he was employed by Christian Dior, the most successful fashion designer of the period. Although also Dior was homosexual, the relationship with his young assistant was of a strictly professional nature. After Dior's death in 1957, the 21-year-old Saint Laurent was appointed chief designer of the Dior company, then France's largest and most prestigious fashion house.

In 1958, Saint Laurent met and fell in love with the entrepreneur Pierre Bergé. his lifelong personal association rapidly became also a professional one, as Bergé assumed the financial, marketing and day-to-day affairs of a new venture, established in 1961, and centered around the haute couture house named after Saint Laurent.

The creation of an international chain of boutiques, retailing exclusive, ready-made garments under the label Saint Laurent Rive Gauche (established in 1966) was the best organised and most successful effort among their Paris contemporaries.

Other areas in which Saint Laurent has achieved considerable sucess include theatre and film design, as well as men's fashion. In spite of all his success, Saint Laurent was painfully shy and reclusive by nature. In 1983, Saint Laurent became the first living fashion designer to be honored by the Metropolitan Museum of Art with a solo exhibition. In 1985, then President of France, François Mitterand, decorated Saint Laurent with the Knighthood of the Legion of Honor.

He came out in 1991. In 2001, he was awarded the rank of Commander of the Légion d'Honneur by French president Jacques Chirac. He retired in 2002 and became increasingly reclusive, living at his homes in Normandy and Morocco with his pet French Bulldog Moujik. He also created a foundation with Bergé in Paris to trace the history of the house of YSL, complete with 15,000 objects and 5,000 pieces of clothing. In 2007, he was awarded the rank of Grand officier de la Légion d'honneur by French President Nicolas Sarkozy.

He died June 1, 2008 of brain cancer at his residence in Paris. According to The New York Times, a few days before he died, Saint Laurent and Bergé were joined in a same-sex civil union known as a Pacte civil de solidarité (PACS) in France.

In February 2009, an auction of 733 items was held by Christie's at the Grand Palais, ranging from paintings by Picasso to ancient Egyptian sculptures. Saint Laurent and Bergé began collecting art in the 1950s. Before the sale, Bergé commented that the decision to sell the collection was taken because, without Saint Laurent, "it has lost the greater part of its significance," with the proceeds proposed for the creation of a new foundation for AIDS research.