Trust is commonly considered a foundation of multilateral diplomacy. Amidst concerns about eroding trust in this realm, due to a ‘crisis’ of multilateralism and ‘hollowing out’ of diplomacy in a socially distanced world, it is surprising that our knowledge of the role trust plays in everyday multilateral diplomacy remains limited at best. In this article, I explore how trusting relations affect multilateral diplomatic practice. I construct a novel theoretical framework that centres on the notion of ‘vitality’—a useful metaphor to capture the lively character of trusting relations and how they differ in what I call intensity, shape and age. I use this framework to analyse the workings of trust in diplomatic practice, based on empirical material gathered over three years (2018–2021) at the Council of the European Union. Contrary to what is often assumed, I find that trusting relations as such do not unequivocally enable smooth decision-making and can also hinder cooperation. We can understand this, I argue, by grasping the social opportunities and constraints that arise from trust ‘climates’ as constituted by configuring trusting relations. Overall, the analysis unpacks complexities in the connection between trust and cooperation in multilateralism. The analytical vocabulary offered in this article allows both scholars and practitioners to comprehend the manifold ways in which trust matters in multilateral diplomacy.