The article contends that an important but overlooked explanation for the European Union's resilience in the past decade in the face of several existential crises has been the informal instrumental leadership roles played by EU institutional actors collaborating with each other. In this article, a theoretical framework is developed that can explain why EU governments, facing a crisis, would choose to informally delegate leadership tasks to a set of EU institutional actors. A three‐part mechanism of collaborative instrumental leadership provided by institutions is devised that explains why governments informally delegate leadership tasks to EU institutions, and the effects of this informal delegation. The core of the article is a process‐tracing case study that explores how collaborative instrumental leadership actually works. The case selected is the British renegotiation of their terms of membership in 2015–2016. While the case has become more‐or‐less forgotten because the shock ‘no’ vote in the June 2016 Brexit referendum made its terms moot, the deal included quite exceptional reform proposals in which the EU bent over backwards to accommodate the United Kingdom, perhaps even going beyond the bounds of the EU Treaties themselves in the issue of immigration. Given this, analysing how collaborative instrumental leadership supplied by institutions contributed to producing the ambitious deal can shed light on the processes whereby intractable problems in the EU have been solved in the past decade.