George Kisevalter was born on 4 April, 1910, in St. Petersburg, Russian Empire, the son of an Imperial Russian Army munitions expert, and grandson of a Russian deputy finance minister. In 1915, Kisevalter's father, accompanied by his family, was sent to the United States in order to purchase weapons for the Russian military, however, during the extensive trip the Bolshevik Revolution occurred two years later. This forced the Kisevalters to remain in the United States, where they eventually took US citizenship, and settled in New York City. The young George attended Stuyvesant High School, and in 1926 he entered Dartmouth College to study engineering, where among his classmates was Nelson Rockefeller.
Kisevalter spent much of World War II as an army officer involved in supporting the Soviet war effort through the Lend-Lease program. His first experience with intelligence came in 1944 when, as a fluent Russian speaker, he was assigned to military intelligence in order to work on Soviet intelligence projects. Due to Kisevalter's growing expertise in Soviet matters, as well as his German language skill, he was one of the officers who interviewed Major General Reinhard Gehlen, after Gehlen had surrendered to the US military. Gehlen had been Nazi Germany's chief of intelligence for the Eastern Front, and was also well versed in Soviet military and political affairs.
Kisevalter had a brief civilian career before joining the CIA, civilian foreign intelligence service of the United States federal government. By 1953, Kisevalter was a branch chief in the Soviet Division of the Directorate of Operations when Major Pyotr Semyonovich Popov of GRU, the foreign military intelligence agency of the Soviet Army, contacted American intelligence in Vienna, Austria, and offered to spy for the United States. Kisevalter was selected as Popov's handler, and spent the next five years in Vienna handling Popov, who provided the United States with detailed information on Soviet military plans and capabilities. During the period when he spied for the United States, Popov was considered to be "the CIA's most important agent." until capture and subsequent execution in 1959.
In 1961, Kisevalter was assigned to handle another GRU member, Colonel Oleg Penkovsky, who had also volunteered to spy. For almost two years Kisevalter and the British Secret Intelligence Service (MI-6) jointly handled Penkovsky, who provided them with vital information on Soviet missile capabilities. Penkovsky's information was critical to the resolution of the Cuban Missile Crisis, however in 1962, Penkovsky was arrested by the Soviet KGB and subsequently executed.
After Penkovsky's execution in 1963, Kisevalter continued to be involved in agent recruitment and handling, including the cases of KGB walk-ins Anatoliy Golitsyn and Yuri Nosenko. Golitsyn's information precipitated a mole hunt by the CIA's counterintelligence chief, James Jesus Angleton. Golitsyn also claimed that Yuri Nosenko was in fact a KGB plant, which led to Nosenko's incarceration in solitary confinement for several years. Kisevalter apparently "never accepted the case for a mole in the CIA or the argument that Nosenko was planted by the KGB".
Kisevalter's final assignment before his retirement in 1970 was training new CIA operations officers, and received the CIA's highest award, the Distinguished Intelligence Medal. In 1997, when the CIA celebrated its 50th anniversary, Kisevalter was designated one of its 50 Trailblazers. He is buried at Arlington National Cemetery.