ObjectiveSmall Island Developing States (SIDS) struggle with implementing multisectoral tobacco control measures, and health sector actors often lack capacity to forge multisectoral commitment. This study aims to explore the sources and dynamics of authority that can enable multisectoral collaboration despite the divergence of policy agendas in tobacco control.MethodsWe applied a qualitative, explorative case study design, with data collection and analysis guided by an analytical framework that identifies sources and dynamics of authority. Seventy interviews were conducted in Fiji and Vanuatu between 2018 and 2019.ResultsThe key features shaping multisectoral coordination for tobacco control in Fiji and Vanuatu are the expert, institutional, capacity-based and legal authority that state and non-state actors have in tobacco governance. The amount of authority actors can secure from these sources was shown to be influenced by their performance (perceived or real), the discourse around tobacco control, the existing legal tools and their strategic alliances. SIDS vulnerabilities, arising from small size, isolation and developing economies, facilitate an economic growth discourse that reduces health sector actors’ authority and empowers protobacco actors to drive tobacco governance.ConclusionsOur results highlight the need for terms of engagement with the tobacco industry to enable governments to implement multisectoral tobacco control measures. Expanding assistance on tobacco control among government and civil society actors and increasing messaging about the impact of economic, trade and agricultural practices on health are essential to help SIDS implement the Framework Convention on Tobacco Control.