We analyse the politics of unilateral secession in the European Union (EU), focusing on the Catalan secessionist conflict. Building on a triangulation strategy, within which primary data are cross-checked through semi-structured expert interviews, we examine how the involved central state and secessionist sub-state actor fought for the support of the supranational party within the EU's multilevel framework. We make two entrenched contributions. We find that the Spanish government succeeded in securing the status quo, not only because of its relations within the bigger European party groups and the benevolent support of EU member states, but also because of the secessionist-restraining nature of the EU. The EU switched from the position of non-intervention towards one of open support for the central state government, and as a result it has developed an informal framework which could deter future unilateral secession intentions.