Delon was born in Sceaux, Île-de-France, not far from Paris. His parents, Édith and Fabien Delon, divorced when Delon was young. Both remarried, and Delon has a half-sister and two half-brothers. He attended a Roman Catholic boarding school, the first of several schools from which he was expelled because of unruly behavior. Teachers once tried to convince him to enter the priesthood because of his aptitude in religious studies.

At 14, Delon left school, and worked for a brief time at his stepfather's butcher shop. He enlisted in the army three years later, and in 1953 was sent to fight in the First Indochina War. Delon has said that out of his five years of military service he spent 11 months in prison for being "undisciplined". After being dishonorably discharged from the army he returned to Paris. He had no money, and got by on whatever employment he could find. He spent time working as a waiter, a porter, and a sales clerk. During this time he became friends with the actress Brigitte Auber, and joined her on a trip to the Cannes Film Festival, where his film career would begin.

At Cannes, Delon was seen by a talent scout for David O. Selznick. After a successful screen test Selznick offered him a contract, provided he learn English. Delon returned to Paris to study English, but when he met French director Yves Allégret, he was convinced that he should stay in France to begin his career. Selznick allowed Delon to cancel his contract, and Allégret gave him his debut in the film Quand la Femme s'en Mêle (When the Woman Butts In). Delon then got to show a comedic aspect of himself in the film Faibles Femmes (Women Are Weak). This was also the first of his films to be seen in America, where it became a success.

In 1960, Delon appeared in René Clément's Purple Noon, which was based on the Patricia Highsmith novel The Talented Mr. Ripley. He played protagonist Tom Ripley to critical acclaim. He then appeared in Luchino Visconti's Rocco and His Brothers.

He was awarded the Best Actor César Awards (French equivalent of Oscars) for his role in Bertrand Blier's Notre histoire (1984). Then a string of box office failures followed in the late 1980s and 1990s, culminating in the failure of Patrice Leconte's Une chance sur deux. Delon announced his decision to give up acting in 1997, although he still occasionally accepts roles.

In 1990, he worked with auteur Jean-Luc Godard, on Nouvelle vague, in which he played twins. In 2003, the Walter Reade Theater showed a series of Delon's films under the aegis, Man in the Shadows: The Films of Alain Delon.

Since the formation of a perfume label in his name, Delon has had a variety of products sold under his name including clothing, eyewear, stationery and cigarettes.

Delon's sunglasses brand became particularly popular in Hong Kong after actor Chow Yun Fat wore them in the 1986 crime film A Better Tomorrow (as well as two sequels).