Since the 2015 parliamentary elections in Poland, the government led by the Law and Justice party (PiS) has sought to win two interwoven battles: the restoration of ‘a strong state’ internally and ‘regaining sovereignty’ in the country’s relationship with the EU. By examining the 2015 constitutional crisis in Poland, this article seeks to understand how and why a domestic dispute over the nomination of constitutional judges has transformed into a conflict of sovereignty in the EU polity. The paper shows that the claims to sovereignty of political, social, and legal actors reflect opposing conceptions of this principle as well as of democracy and the rule of law. PiS’ understanding of State sovereignty is rooted in the past, echoes its Hobbesian conception, and is reminiscent of Carl Schmitt’s notion of the political and of democracy. In 2015, this conception was pitted against the supremacy of the Constitution (legal sovereignty) and the ideal of shared sovereignty. Drawing on 20 parliamentary debates, this paper shows that the 2015 Polish constitutional crisis encapsulates a conflict of sovereignty over who holds the most legitimate representation of the people and who should have the last word in key political conflicts and constitutional settlements.