This paper discusses how the internationalization of the Brazilian mining corporation Vale S.A, particularly its incursion into Mozambique, has given rise to transnational contestation efforts to resist extraction, from below and along a South-South axis. It does so by approaching the politics and practices of mobilization of the International Articulation of those Affected by Vale (AV), paying special attention to the ties forged between Mozambican and Brazilian civil society. This paper contends that the AV’s transnational activism and mobilization strength is context-dependent and defined by given political opportunities, which affect actors’ capacity and propensity to mobilize against Vale. Focusing on the determinants shaping the AV’s engagement in contentious politics, this paper analyzes which political opportunities have contributed to its establishment, how resources were mobilized to pursue transnational collective action and to push for change, and to which extent shifting political and economic circumstances in Brazil and Mozambique have affected mobilization prospects. This paper provides a critical, bottom-up perspective on the outward expansion of Vale as a Southern mining multinational and contributes to the literature on resistance to extractivism, exploring such dynamics in a transnational and South-South configuration.