<p>Cities are increasingly recognised as key agents in international relations, yet they are often overlooked as independent actors with their own priorities. By adapting the concept of strategic partnerships (SPs), originally devised for state actors, this article conceptualises city diplomacy as a distinctive, subnational SP. We argue that non-material factors—including mutual trust, shared objectives, and spatial synergies—are key in enabling effective cooperation among municipal actors. Drawing on 29 interviews conducted in the UK and China, participant observations, and policy documents, our investigation of the Manchester–Wuhan sister-city partnership, one of the longest-standing UK–China collaborations, illustrates how local partnerships can transcend national constraints to pursue shared priorities. By foregrounding these non-material yet pivotal drivers, our analysis reveals how subnational partnerships remain adaptable and resilient amid shifting geopolitical contexts. In doing so, we challenge state-centric assumptions in International Relations, highlighting the transformative potential of city diplomacy in addressing global development challenges. This research contributes to ongoing debates on the role of the nation-state in contemporary international relations by illustrating how city-level SPs can transcend national-level geopolitical tensions.</p>