Generating momentum for activist campaigns on complicated economic issues is difficult, especially in a transnational context. So, how did activists get action on tax justice and create a movement that has changed global tax policy? Drawing on 20 years of para-ethnographic fieldwork with the Tax Justice Network, we suggest that activists initially engaged in ‘identity switching’ tactics to access professional or policy arenas from a footing in one identity, to then switch identities to activate policy shifts. A first-generation leveraged multiple professional identities to access forums, build credibility and introduce a tax lexicon to activists and policymakers. These tactics were not, however, replicable, leading a second generation to concentrate on ‘identity fixing’, including professionalization and a tightening of organizational strategy over access and activation points. Here we theorize identity switching and fixing as underappreciated micro-foundations of transnational activism and demonstrate their importance for global economic justice.