The article traces the evolution of the legal competences of the European Union (EU) in international investment regulation from the Spaak Report (1956) to the Lisbon Treaty (2009). It focuses on the question why and how the EU gradually acquired legal competences in this key domain of global economic governance. The analysis suggests that Commission entrepreneurship and spill-overs from other EU policies were the most important factors fuelling the extension of the EU’s legal competences. The Member States, on the other hand, sought to prevent a competence transfer. European business – arguably the main stakeholder – was mostly uninterested or divided regarding the EU’s role in international investment policy. The findings have implications for our perception of business lobbying in international investment policy and potentially for the legal interpretation and delimitation of the EU’s new competences.