After the war Robertson joined the Central Intelligence Agency. He was employed as a counter-intelligence agent and was involved in what became known as Executive Action (a plan to remove unfriendly foreign leaders from power). This including a coup d'état that overthrew the Guatemalan government of Jacobo Arbenz in 1954 after he introduced land reforms and nationalized the United Fruit Company.
Robertson became a CIA outcast after he was found responsible for ordering the bombing of a British ship which he had mistakenly identified as Russian. He moved to Nicaragua where he worked as an adviser to the government of Anastasio Somoza.
Robertson returned to the CIA before the Bay of Pigs operation. He commanded the supply ship Barbara J and disobeyed orders by landing in Cuba with Brigade 2506. Afterwards Roberson became a member of staff at CIA's JM WAVE station in Miami.
In the winter of 1962 Eddie Bayo claimed that two officers in the Red Army based in Cuba wanted to defect to the United States. Bayo added that these men wanted to pass on details about atomic warheads and missiles that were still in Cuba despite the agreement that followed the Cuban Missile Crisis.
Bayo had originally fought with Fidel Castro against Fulgencio Batista. He disagreed with Castro's policies after he gained power and moved to Miami and helped establish Alpha 66. His story was eventually taken up by several members of the anti-Castro community. William Pawley became convinced that it was vitally important to help get these Soviet officers out of Cuba. To help this happen he contacted James Eastland, the chairman of the Senate Internal Security Subcommittee.
William Pawley also contacted Ted Shackley, head of the CIA's JM WAVE station in Miami. Shackley decided to help Pawley organize what became known as Operation Tilt. He also assigned Robertson to help with the operation. David Sanchez Morales, another CIA agent, also became involved in this attempt to bring out these two Soviet officers.
In June, 1963, a small group, including Robertson, John Martino, William Pawley, Eddie Bayo and Richard Billings, a journalist working for Life Magazine, secretly arrived in Cuba. They were unsuccessful in their attempts to find these Soviet officers and they were forced to return to Miami. Bayo remained behind and it was rumoured that he had been captured and executed. However, his death was never reported in the Cuban press.
Some researchers such as James Richards have argued that photographic evidence suggests that Robertson was in Dealey Plaza during the assassination of John F. Kennedy. Others involved in the plot include James Arthur Lewis, Roy Hargraves, Edwin Collins, Steve Wilson, Gerry P. Hemming, David Morales, Herminio Diaz Garcia, Tony Cuesta, Eugenio Martinez, Virgilio Gonzalez and Felipe Vidal Santiago.