The article, written on the basis of Serbian sources and documents of the US Central Intelligence Agency, is devoted to the figure of Sava Kosanović, a politician who was active during the two periods, that of the First Yugoslavia between the wars, and that of the Second Yugoslavia under Tito’s communist rule. The author pays special attention to the role of Kosanović during the Second World War, when, as a member of the Yugoslav government in exile, he criticized the nationalist line of supporters of King Peter II and supported the communist partisans, contributing to the creation of a positive image of this movement and its leader, Josip Broz Tito. In this regard, on the basis of documents of the American counterintelligence, or the Venona project, the question is raised whether Kosanović was possibly connected to the Soviet secret service. His activities as Ambassador of Yugoslavia to the United States (in 1946–1949) are also considered. During this time, he managed to slightly improve the relations between the two countries that were damaged after the war and to start a dialogue with the Americans after the Soviet-Yugoslav conflict of 1948, aimed at providing assistance to Belgrade from Western states.