The objective of this thesis is to extend the knowledge of the role of August Košutić in the political events during the Second World War and the post-war period (1941-1964) based on the accessible archival database, published documents, the press and the results of former historiographical research, by this contributing to an important theme of Croatian history and inspiring researchers for further study of the abovementioned period. The research is greatly based on archival database which was couple of years ago still not procurable for researchers. Among the fonds predominate the fonds of the Croatian State Archives (CSA) in Zagreb, particularly the Fond of the Republican Secretariate fot Internal Affairs of the Socialist Republic of Croatia, State Security Service (Fond RSIF SRC, SSS) and the Fond of the Central Committee of the League of Communists of Croatia (Fond CC LCC). Košutić as vice-president of the strongest Croatian political party of the pre-war period led CPP through the Second World War and the post-war period. In wartime, when only the combination of military and political power granted results, Košutić unsuccessfully attempted to retain the CPP's pre-war relevance in negotiations with all warring parties. The post-war period brought waves of repression of the communist regime with the objective of complete annihilation of the party. Košutić succeeded by passisivisation of the party to prevent her physical annihilation, but he couldn't do more than that and CPP politically expired, with Košutić at the head of the party until his death.