ABSTRACT Diffusion is key to understanding the transnational spread of social movements. Given its relevance, scholarship in the field of social movements has explored many different dimensions of the diffusion process. Most of these studies, however, focus on the diffusion process during movements’ intense periods of visibility. In contrast, this paper explores an understudied facet of transnational diffusion: its links to the latency of social movements in the context of anti-immigration mobilisation. Using an original theoretical perspective, it investigates the role of transnational diffusion in feeding far-right mobilisation outside their peak, disclosing how submerged networks survive during their invisible phases. Drawing on novel empirical data collected from in-depth interviews with Portuguese far-right activists, we show how the lack of politicisation of migration in Portugal pushes anti-immigration mobilisation into a permanent state of latency, and how transnational diffusion emerges as a key mechanism for the maintenance of their frames. Moreover, our analysis illuminates the agency of Portuguese anti-immigration activists in the transnational diffusion process in adopting and adapting frames from successful movements elsewhere. Lastly, we offer an innovative contribution to far-right scholarship, by exploring the under-researched context in Portugal, offering valuable insights applicable to similar cases.