Maclean's drinking became problematic once again as he vociferously denounced the capitalism of the west and espoused the virtues of communism during dinner parties and formal affairs. Word of his behavior circulated around London and in January 1951, Kim Philby learned more about the information in the Venona documents and worried that he was in impending jeopardy of being arrested. Concerned that telephone calls or cables to London might be intercepted, Philby sought another way to warn Maclean. Guy Burgess, also enjoying a reputation as a drunkard, engaged in sufficient misbehavior to merit being sent home from the United States where he was serving with the British embassy. Burgess immediately informed Anthony Blunt of Maclean's impending danger and Blunt likewise informed their Soviet handler Yuri Modin.

Modin immediately set into motion an escape plan and three days before Maclean was to be arrested by MI5, Burgess drove him to Southampton where the two climbed aboard a ferry boat, the S.S. Falaise that took them to St. Malo. Eventually the two made their way to Moscow where they hailed as heroes to the Soviet people. Maclean was given the rank of KGB Colonel. He was joined in September by his wife and children. Maclean and Burgess were put on display for the western press by the Soviet government in 1956. Maclean worked hard to adapt to the Soviet culture and was rewarded by the government with salary and accommodations.

He wrote several publications on economics and was published in the Soviet Union and Britain. In 1966, Melinda Maclean began an affair with Kim Philby, Philby having defected in early 1963. She moved in with him two years later but returned to the United States in 1979.

Donald Maclean died of a heart attack on March 6, 1983. His ashes were buried in England months later.