After starting his own film club in 1948, Truffaut met André Bazin, who would have great effect on his professional and personal life. Bazin was a critic and the head of another film society at the time. He became a personal friend of Truffaut's and helped him out of various financial and criminal situations during his formative years.
Truffaut joined the French Army in 1950, aged 18, but spent the next two years trying to escape. Truffaut was arrested for attempting to desert the army. Bazin used his various political contacts to get Truffaut released and set him up with a job at his newly formed film magazine Cahiers du cinéma. Over the next few years, Truffaut became a critic (and later editor) at Cahiers, where he became notorious for his brutal, unforgiving reviews. He was called "The Gravedigger of French Cinema" and was the only French critic not invited to the Cannes Film Festival in 1958. He supported Andre Bazin in the development of one of the most influential theories of cinema itself, the auteur theory.
In 1954, Truffaut wrote an article called "Une Certaine Tendance du Cinéma Français" ("A Certain Trend of French Cinema"), in which he attacked the current state of French films, lambasting certain screenwriters and producers. The article resulted in a storm of controversy. Truffaut later devised the auteur theory, which stated that the director was the "author" of his work; that great directors such as Renoir or Hitchcock have distinct styles and themes that permeate all of their films. Although his theory was not widely accepted then, it gained some support in the 1960s from American critic Andrew Sarris. In 1967, Truffaut published his book-length interview of Hitchcock, Hitchcock/Truffaut (New York: Simon and Schuster).
After having been a critic, Truffaut decided to make films of his own. He started out with the short film Une Visite in 1955 and followed that up with Les Mistons in 1957. After seeing Orson Welles' Touch of Evil at the Expo 58, he was inspired to make his feature film debut in 1959 with Les Quatre Cents Coups (The 400 Blows).This film was an instant success and won him a prize at the Cannes Film Festival This film and the following films were successful even with the low budget he had to make the films.
He was also notably one of the main stars in Steven Spielberg's 1977 film Close Encounters of the Third Kind, where he played scientist Claude Lacombe.Truffaut was married to Madeleine Morgenstern from 1957 to 1965, and they had two daughters, Laura (born 1959) and Eva (born 1961). Madeleine was the daughter of Ignace Morgenstern, managing director of one of France's largest film distribution companies, and was largely responsible for securing funding for Truffaut's first films. While he had affairs with almost all of his leading ladies - in 1968 he was the fiancé of Claude Jade - Truffaut and actress Fanny Ardant lived together from 1981 to 1984 and had a daughter, Joséphine Truffaut (born 28 September 1983).