Though, Camus is one of those who rejected the etiquettes of atheis existentialism but some people still refer to Camus as an atheist existentialis. Is he truly an atheist existentialist? Whic works proved it.
Albert Camus is "sui generis" or "in a category of his own". He is not able to be branded an existentialist but he sounds very similar to them. He vehemently rejected the title. Also he made the famously cryptic remark "I do not believe in God and I am not an atheist." Thus he is usually called an agnostic. Camus managed to avoid classification by his own insistence that he was opposed to existentialism (especially the darker more nihilistic forms of it) and that he is not an atheist. He certainly does sound like an atheist existentialist at points doesn't he?
Camus didn't want to be known as an existentialist. Nevertheless, on most philosophical definitions of existentialism and atheism, Camus is properly categorized as an atheist existentialist. The works where the theme of the absurdity of life without God comes out most clearly are Betwixt and Between (1937), Nuptials (1938), The Stranger (1942), and The Myth of Sisyphus (1942).
In 1948, Camus gave a talk before the monks of the Dominican Monastery of Latour-Mauborg (published as "The Unbeliever and Christians," Resistance, Rebellion and Death. Trans. Justin O'Brien. Vintage, 1974. pp. 69-74.). Here, Camus articulates what he shares with Christians--a revulsion from evil; and what he doesn't share with Christians: while Christians are pessimistic about man but optimistic about human destiny, Camus is optimistic about man but pessimistic about human destiny.