In 2017, member states established the European Public Prosecutor's Office (EPPO), an EU body investigating and prosecuting offences against the EU financial interests. This article analyses the relation between the institutional design of the EPPO and sovereignty concerns of member states. Combining the core state powers framework with literature on Council negotiation dynamics, it argues that the Council was divided on the question of how far-reaching the authority of this new body vis-à-vis member states should be or to what extent member states should retain control over the body. A qualitative discourse analysis shows that the competition between states sharing a supranational position regarding the EPPO and those sharing an intergovernmental position resulted in the creation of a complex and ambiguous body. These findings contribute to the literature on agencification of Justice and Home Affairs as well as, more broadly, to scholarship on the construction of new types of authority.