This paper examines the relationship between the institutional set-up of the EU policy-making process and the international actorness of the EU in two cases: the establishment of the International Criminal Court (ICC) and the negotiations in the United Nations Framework Convention on Climate Change (UNFCCC) on the implementation details of the Kyoto Protocol. In both cases, the EU policy-making process is distinctly intergovernmental with a limited role for the supranational EU institutions (the European Parliament and the European Commission) and a large role for EU member states and the Council Presidency. Yet, in both cases, the EU operates with a high degree of international actorness. We argue that this is so not only because member states had similar preferences on the issue of climate change and international criminal justice, and because formal rules, legal competences and decision-making procedures had a mediating effect. The high degree of international actorness in both cases can also be explained by processes of social interaction amongst EU member states and between EU member states and non-EU and non-state actors through which preferences converged.