Jean-Paul Sartre’s letter informing the Swedish Academy that he would decline the Nobel prize, were it to be offered to him, arrived after the jury had already decided upon the French existentialist as their winner, newly opened archives confirm.

Sartre was named as the Nobel laureate for literature in 1964, praised by the academy “for his work which, rich in ideas and filled with the spirit of freedom and the quest for truth, has exerted a far-reaching influence on our age”. But the author of Huis Clos and La Nausée declined the award, later explaining his belief that “a writer who adopts political, social, or literary positions must act only with the means that are his own – that is, the written word”, and that “all the honours he may receive expose his readers to a pressure I do not consider desirable”.

Because the Swedish Academy keeps all information about nominations and selections for the prestigious award secret for 50 years, the details behind the procedure have been hazy. But the archives have now been opened, and reveal that Sartre’s 14 October letter to the committee asking them not to choose him as winner arrived once the decision had been made.

According to Swedish paper Svenska Dagbladet, the jury had decided to propose Sartre as their winner on 17 September 1964; other names in the running that year included Russian writer Mikhail Sholokhov – who would win the following year – and British poet WH Auden, who never took the Nobel.

In total, there were 76 candidates that year, the Nobel academy has revealed, of which 19 were new nominations. Svenska Dagbladet says that there was ambivalence around the choice of Sartre, and speculates that if his letter – written after an article in the French press alerted Sartre to the possibility of winning the Nobel – had arrived before the September meeting, the committee might have swung another way. Sartre had written – “emphatically”, according to the Swedish paper – that he “did not wish to be included on the list of prize winners, neither in 1964 nor in the future, and that he would not be able to accept such an award”.

But the committee went ahead with their decision, and Sartre was true to his word and turned down the prize. He is the only literature laureate known to have voluntarily declined the award. In 1958, Russian writer Boris Pasternak was named winner of the Nobel; he initially accepted it, but “was later caused by the authorities of his country to decline the prize”.

In a statement to the Swedish press in 1964, translated into English in the New York Review of Books, Sartre said he had “always declined official honours”, including France’s Legion of Honour.

“The writer who accepts an honour of this kind involves as well as himself the association or institution which has honoured him,” he said at the time. “The writer must therefore refuse to let himself be transformed into an institution, even if this occurs under the most honourable circumstances, as in the present case.”

But Sartre said that he had been “tortured” by the amount of money with which the prize comes – at that time it was 250,000Kr. “Either one accepts the prize and with the prize money can support organisations or movements one considers important – my own thoughts went to the Apartheid committee in London,” he said. “Or else one declines the prize on generous principles, and thereby deprives such a movement of badly needed support.

“But I believe this to be a false problem. I obviously renounce the 250,000 crowns because I do not wish to be institutionalised in either East or West. But one cannot be asked on the other hand to renounce, for 250,000 crowns, principles which are not only one’s own, but are shared by all one’s comrades. That is what has made so painful for me both the awarding of the prize and the refusal of it I am obliged to make.”