Thanks to its innovative supranational features, the European Coal and Steel Community is widely recognized as the cornerstone of the European integration process. This article offers an alternative history of the European Coal and Steel Community's origins by highlighting the role of transnational expertise and public diplomacy. More precisely, this study seeks to demonstrate that the policies carried out by Jean Monnet, the mastermind of European Coal and Steel Community's blueprint, originated from the plans elaborated by the New York-based think tank Council on Foreign Relations. While advising the Roosevelt and Truman administrations, the Council on Foreign Relations formed a policy network with European policymakers sharing similar political values and goals. Although the interactions between these figures have never been studied, new findings reveal that the Council on Foreign Relations–Monnet partnership proved instrumental in improving inter-Allied coordination, managing postwar recovery and framing the idea of European unity. Eventually, the Council on Foreign Relations helped Monnet to define, adjust and promote the European Coal and Steel Community Treaty draft. In this perspective, the foundation of the first European institution derived from a long-term strategic design rooted in wartime planning and transatlantic diplomatic exchanges.