The main purpose of this paper is to answer the question of whether the communist authorities’ references to the March Constitution in the 1944 Manifesto of the Polish Committee of National Liberation had a real impact on the shaping of the political system in Poland in 1944–1947. The authorities paid particular attention to the illegal adoption of the April Constitution, refusing its binding force, thus denying the legal activity of the Polish government in exile. The principles on which the March constitution was based will be discussed and then compared with the principles declared by the new authorities and their application in practice. Attention will be paid to the understanding of these principles that differs from the meaning adopted in the interwar period.