This article presents an empirical case study of a type of nonstate actor largely overlooked in the IR literature on transnationalism: the diaspora or transnational ethnic actor. Building upon findings from contentious politics or social movements scholarship, I highlight the nexus of domestic and transnational politics by demonstrating how actors form ethnic networks and utilise transnational opportunities to pursue political goals in various states. Specifically, I argue that the formation of ethnic networks in the Tamil diaspora has enabled the Liberation Tigers of Tamil Eelam (LTTE) or ‘Tigers’ to engage in protracted insurgency against the Sri Lankan government army. Whereas traditional contentious politics scholarship is unable to explain the longevity and intensity of that conflict, a consideration of the transnational dimension provides new insight into how ethnic conflicts may be sustained. The combination of greater political freedom, community organising and access to advanced communications and financial resources in receiving states has allowed Tamil separatists in the diaspora to maintain ‘transnational ethnic networks’ which are in turn used to mobilise funds that have prolonged the secessionist campaign in Sri Lanka.