In this article, the connections of Gyula Moravcsik (1892–1972), a great Hungarian Byzantinist, with Soviet historical science are reconstructed. Chronologically, the article is concerned with the period after World War Two, when Hungary fell into the orbit of Soviet political influence. However, the article outlines the origins of the formation of Moravcsik’s contacts and explains the reasons for his interest in the work of Russian scholars, both of which began during the First World War, and then developed in the 1920s and 1930s. This article shows that politics had a direct impact on the dynamics of Moravcsik’s contacts with Soviet scholars; immediately after the end of Second World War, they were curtailed by ideological campaigns in the USSR and the atmosphere of late Stalinism, and only revived during the Thaw. Using specific examples, the main methods of intellectual interaction between Moravcsik and his colleagues from the USSR are demonstrated. The Hungarian scholar provided them with supporting information, helped them to study foreign historiography, and contributed to the publication of works by Soviet scientists in Hungary, and Hungarian works in the USSR. Moravcsik’s work found many favourable responses in the USSR, and he himself closely followed the Soviet scientific literature and published his works in Russian, in particular in the famous review Vizantiiskii Vremennik. The circle of Soviet scholars with whom Moravcsik established the closest and strongest relations are outlined (including Boris Gorianov, Evgenii Kosminskii, Gennadii Litavrin, Nina Pigulevskaya, and Zinaida Udalʹtsova). It is shown that Moravcsik, even during the Cold War, advocated the development of international scientific relations and promoted the achievements of Russian and Soviet Byzantine studies. Moravcsik has always divided science and politics, and therefore the dramatic turns of the history of the twentieth century could not shake his positive and respectful attitude towards Russian historical science. Despite the fact that not all the possibilities of Moravcsik’s cooperation with Soviet scholars were realised, the results of his contributions should be considered successful.