Mr Reynolds, who said he was able to access a classified KGB file smuggled out of Moscow, claims the Pulitzer prize-winning author was recruited in 1940 by the predecessor to the KGB known as NKVD.
The document reportedly revealed that Hemingway was given the codename “Argo” after he was recruited by Jacob Golos, a top NKVD official in New York.
“Argo did not give us any political information, though he repeatedly expressed his willingness and desire to help us,” the Soviet file reportedly reads.
Mr Reynolds, a military historian, said he felt “physically ill” when he stumbled across the detail linking Hemingway to Stalin.
“The idea of Ernest Hemingway having done anything with the Soviets, especially having been recruited by the Soviets, was really difficult for me to absorb,” he told US broadcaster CBS.
“What I found was the record of Hemingway having agreed to a recruitment by the NKVD, which is the predecessor to the KGB. That’s like a pivotal moment in the spy business. It’s like a sale to a realtor.”
Reynolds also detailed Hemingway’s special relationship with American security agencies, including the FBI, State Department, Office of Naval Intelligence (ONI) and the Office of Strategic Services (OSS) - the CIA’s predecessor.
“[His dalliance with the NKVD] influenced many of the decisions he made during his last 15 years: where he lived, what he wrote, and how he acted,” Mr Reynolds told MailOnline.
“This chain of events even played a role in his suicide in 1961. Much of the drama played out in his mind, where he magnified it out of proportion.”
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