Arkady Nikolayevich Shevchenko (October 11, 1930 – February 28, 1998) was a Soviet diplomat who was the highest-ranking Soviet official to defect to the West.

Shevchenko joined the Soviet diplomatic service, the Ministry of Foreign Affairs, as a young man and rose through its ranks to become an advisor to Foreign Minister Andrei Gromyko. In 1973, he was appointed Under-Secretary-General of the United Nations (USG). During his assignment at the UN headquarters, in New York City, Shevchenko began to pass Soviet secrets to the CIA because he could not objectively fulfill his mission of impartiality to the United Nations. In 1978, he cut his ties to the Soviet Union and defected to the United States, where he lived for the rest of his life.

Shevchenko was born in the town of Horlivka, in the east of Ukraine, and when he was five his family moved to Yevpatoria, a resort town in Crimea, on the Black Sea, where his father, a physician, was the administrator of a tuberculosis sanatorium. When Crimea was invaded by German forces in 1941, he, his mother, and the sanatorium patients were evacuated to Torgai, in the Altay Mountains of Siberia. The family was reunited in 1944 after the Germans retreated from Crimea. He later recalled how his father attended the Yalta Conference, in part on orders to observe and report on the health of US President Franklin Roosevelt.

Shevchenko graduated from secondary school in 1949 and that year was admitted to Moscow State Institute of International Relations. He studied Soviet law and Marxist, Leninist and Stalinist theory and was trained to become a foreign service diplomat. He married Leongina (Lina), a fellow student, in 1951. He completed the program in 1954 and continued with graduate studies.

In 1956, Shevchenko joined the Ministry of Foreign Affairs as an attaché and was assigned to the OMO (Russian: Отдел Международных Организаций Министерства Иностранных Дел СССР, Department of International Organizations at the Ministry for Foreign Affairs of the USSR), a branch of the Foreign Ministry dealing with the United Nations and NGOs. In 1958, he was sent to New York City on a three-month assignment to represent the Soviet Union at the annual UN General Assembly as a disarmament specialist.

Shevchenko attended the 1962 Geneva Committee on Disarmament Negotiations as a member of the Soviet delegation. The next year, he accepted an assignment as Chief of the Soviet Mission's Security Council and Political Affairs Division at the United Nations. Since that was a permanent posting, his family accompanied him to New York City. He continued in that post until 1970 when he was appointed advisor to Andrei Gromyko. His duties covered a broad range of Soviet foreign policy initiatives.

In his disarmament role, Shevchenko had a close view of the Cuban Missile Crisis and the Soviet leadership's perspective of it. He later described it in an interview with WGBH.

In 1973, Shevchenko was promoted and became an Under-Secretary-General of the United Nations. Although he was nominally employed by the United Nations and owed his allegiance to the international organization, he was in practice expected to support and to promote Soviet aims and policies. He eventually became resentful of the restrictions that his Soviet superiors subjected him to that prevented him from carrying out his duties as an Under Secretary objectively.