Montes was born in West Germany, where her father, Alberto Montes, was posted as a United States Army doctor. Her family was of Asturian origins, and her grandparents had emigrated to Puerto Rico. The family later lived in Topeka, Kansas and then Towson, Maryland, where she graduated from Loch Raven High School in 1975. In 1979 she earned a degree in foreign affairs from the University of Virginia, and in 1988 she finished a master's degree at Johns Hopkins University School of Advanced International Studies.
Montes' brother and sister, Tito and Lucy, became Federal Bureau of Investigation officers and her former boyfriend, Roger Corneretto, was an intelligence officer specializing in Cuba for the Pentagon.
Montes joined the Defense Intelligence Agency (DIA) in September 1985 after working for the United States Department of Justice. Her first assignment was at Bolling Air Force Base in Washington where she worked as an intelligence research specialist. In 1992, Montes was selected for the DIA's Exceptional Analyst Program and later traveled to Cuba to study the Cuban military.
Prior to her arrest, she lived in a two bedroom co-op in Cleveland Park, Washington, DC.
Montes advanced rapidly through the ranks at the DIA and became its most senior Cuban analyst. Her co-workers regarded her as responsible and dependable, and noted her "no-nonsense" attitude. Prosecutors would later allege that Montes was already working for the Cubans when she joined the DIA in 1985.
In their charging documents, federal prosecutors stated:
Montes communicated with the Cuban Intelligence Service through encrypted messages and received her instructions through shortwave encrypted transmissions from Cuba. In addition, Montes communicated by coded numeric pager messages with the Cuban Intelligence Service by public telephones located in the District of Columbia and Maryland. The codes included 'I received message' or 'danger.'
The prosecutors further stated that all of the information was on water-soluble paper that could be rapidly destroyed.
During the course of the investigation against her, it was determined that Montes had passed a considerable amount of classified information to the Cuban Intelligence Directorate, including the identities of four US spies in Cuba. In 2007, American DIA counterintelligence official Scott W. Carmichael publicly alleged that it was Ana Montes who told Cuban intelligence officers about a clandestine US Army camp in El Salvador. Carmichael alleged that Montes knew about the existence of the Special Forces camp because she visited it only a few weeks before the camp was attacked in 1987 by Cuban-supported guerrillas of the Farabundo Martí National Liberation Front (FMLN).
Carmichael, who had led the DIA investigation of Montes, named her as being directly responsible for the death of Green Beret Sergeant Gregory A. Fronius who was killed at El Paraíso, El Salvador, on March 31, 1987 during the FMLN attack. Carmichael characterized the damage Montes caused to the DIA and other US intelligence agencies as "exceptionally grave," and stated that she compromised a "special access program" that was kept even from him, the lead investigator on her case.
In a May 6, 2002 interview with CBS News, former Undersecretary of State John Bolton stated that an official 1998 US government report with significant contributions by Montes concluded that Cuba did not represent a significant military threat to the United States or the region. Bolton alleged that it was not possible to exclude the possibility that the administration of President Bill Clinton may have overlooked Cuba as a potential threat because of Montes' influence and the way she shaped reporting at the DIA.
Carmichael further alleged that, unlike many in the US intelligence community, he believed that Montes' penetration of the DIA was not the exception, but the rule, and that the Cuban intelligence services had multiple spies and moles within US intelligence agencies.
In 2004 a federal indictment alleged that Montes had assistance from another Cuban agent, Marta Rita Velazquez, once a legal officer at the United States Agency for International Development, who was further alleged to have recruited Montes into espionage. The Federal indictment was unsealed in April 2013. Velazquez has been outside the US since 2002, apparently in Sweden, which does not have an extradition treaty with the US for spy cases.
Montes was arrested by the Federal Bureau of Investigation at her office on 21 September 2001. Prosecutors stated that Montes had been privy to classified information about the US military's impending invasion of Afghanistan in October 2001, and that they did not want her revealing this information to potential enemies.
In 2002, Montes pleaded guilty to the charge which could have carried the death penalty, but was sentenced to 25 years in prison in October of the same year after accepting a plea agreement with the US government. According to her lawyer, Plato Cacheris, Montes committed the espionage for moral reasons, as "she felt the Cubans were treated unfairly by the U.S. government."
As of July 2016, Montes is incarcerated at FMC Carswell in Fort Worth, Texas. FMC Carswell is listed by the Federal Bureau of Prisons as a facility located in the northeast corner of the Naval Air Station, Joint Reserve Base, Fort Worth, which provides specialized medical and mental health services to female offenders.
Montes is listed as FMC Register #25037-016. Her tentative release date is listed as July 1, 2023.