Ana Montes, now 65, worked as an analyst for the Defence Intelligence Agency for over two decades while spying for Cuba.
Officials said that she had essentially fully disclosed US spy operations on the island after her detention in 2001.
She was among “the most damaging spies” the US managed to capture, according to one official.
George W. Bush administration’s counterintelligence chief Michelle Van Cleave testified before Congress in 2012 that Montes had “compromised everything – nearly everything we knew about Cuba and how we conducted business there.”
Following her arrest, Montes was charged with providing the names of four US spies and tonnes of top-secret information.
She received a 25-year prison sentence when the sentencing court declared that she had endangered the “nation as a whole.”
However, Montes was driven by philosophy rather than selfish ambition, in contrast to other well-known spies discovered during the Cold War.
Due in part to her hostility to the Reagan Administration’s initiatives in Latin America, she decided to work with Cuban intelligence.
She is thought to have been particularly enraged by US assistance for the Nicaragua Contras, a right-wing rebel group suspected of perpetrating war crimes and other atrocities in the nation, according to a report from the inspector general of the defence department.
In 1984, she expressed concern over US operations in Nicaragua and a fellow student at Johns Hopkins University approached her.
After being introduced to a Cuban intelligence agent, she “unhesitatingly volunteered” to collaborate with the Cubans to “assist” Nicaragua at a dinner in New York City, according to the inspector general’s investigation.
The next year, she went to Havana for training before joining the Defense Intelligence Agency, where she eventually rose to the position of senior analyst for the group’s study of the communist regime on the island.
She communicated with her Cuban handlers through pagers and met with them every few weeks at restaurants in Washington, DC, for nearly two decades.
After US intelligence officials received a report that a federal employee appeared to be spying for Cuba, they finally captured her in September 2001.
She was apprehended by an FBI agent, who noted that she had a stoic demeanour.
After being released, Montes will be under observation for five years, and her internet usage will be tracked.
She won’t be permitted to contact foreign agents or work for the government without authorisation.
Pete Lapp, one of the FBI agents involved in the arrest of Montes, however, told CBS News that he didn’t believe she would make another attempt to get in touch with Cuban spies.