Ray Bradbury was investigated by the FBI during the 1950s, with government agents interviewing his peers and putting him under surveillance before concluding that despite being critical of the US government in his writing, the celebrated writer was never a member of the Communist party.

The 40-page cache of the late science fiction author's FBI files was obtained by the Daily Beast following a Freedom of Information request, and shows the extent to which the FBI had Bradbury in its sights in 1959. "Raymond Douglas Bradbury, a freelance science fiction, television and motion picture scenario writer … has been described as being critical of the United States Government," the FBI wrote on 8 June 1959, before laying out its issue with Bradbury's classic collection of short stories, The Martian Chronicles. The stories "were connected by the repeated theme that earthmen are despoilers and not developers", according to the FBI.

The FBI uncovered the information that "Bradbury has been extremely successful in the writing field". The bureau also discovered "that Bradbury, while a young man, sold papers and did miscellaneous small jobs", and that "in 1942 his writing were beginning to return him a descent [sic] livelihood".

A named source in the file, Martin A Berkeley, told the agents investigating Bradbury that the author "was probably sympathetic with certain pro-communist elements", and that during a discussion about whether Communist party members should be allowed to join the Screen Writers Guild, Bradbury "rose to his feet and shouted 'Cowards and McCarthyites' when the resolution was discussed".

Berkeley, a "self-admitted" former member of the Communist party, went on to tell the FBI "that science fiction may be a lucrative field for the introduction of communist ideologies", and that "some of Bradbury's stories have been definitely slanted against the United States and its capitalistic form of government".

Another informant agreed about the dangerous effects of science fiction, advising "that individuals such as Ray Bradbury are in a position to spread poison concerning political institutions in general and American institutions in particular", and that "Communists have found fertile opportunities for development; for spreading distrust and lack of confidence in America [sic] institutions in the area of science fiction writing". Even worse, "the general aim of these science fiction writers is to frighten the people into a state of paralysis or psychological incompetence bordering on hysteria which would make it very possible to conduct a Third World War which the American people would seriously believe could not be won since their morals had been seriously destroyed".

Bradbury did not help his own cause by taking out an advertisement in the Daily Variety in 1952, in which, according to the FBI documents, he wrote: "I have seen too much fear in a country that has no right to be afraid. I have seen too many campaigns in California, as well as in other states, won on the issue of fear itself, and not on the facts. I do not want to hear any more of this claptrap and nonsense from you. I will not welcome it from McCARTHY or McCARRAN, from Mr NIXON, DONALD JACKSON, or a man named SPARKMAN. I do not want any more lies, any more prejudice, any more smears. I do not want intimations, hearsay or rumour. I do not want unsigned letters or nameless telephone calls from either side, or from anyone."

Despite this, the FBI concluded in 1959 that "no evidences have been developed which indicate he was ever a member of the [ party]".

In 1968, however, it was investigating Bradbury again, looking into a potential trip by Bradbury to the Cultural Congress of Havana in Cuba, the purpose of which was "to obtain unity of action in the anti-imperialist fight". There appeared to be some confusion over the tip received by the federal agency, however: the named individual was one "Roy Bradbury", and after investigating Bradbury's passport file and lacking evidence that he had applied for or travelled to Cuba, it dropped the investigation, deciding not to interview the author. "Due to Bradbury's background as a known liberal writer, vocal in anti-United States war policies, an interview with Bradbury would be deemed unadvisable," an agent wrote.

Sam Weller, Bradbury's biographer, describes the FBI investigation in his book The Bradbury Chronicles. "I remember distinctly his response when I visited him and presented him with the files," Weller told The Daily Beast. "He beamed ear to ear and dismissed it with a wave of his hand and laughed and he said, 'I'll be damned, I've had nothing to hide over the years – what are they going to investigate? What a bore.'"