Despite proliferation of political protest by migrants in recent years, analyses from a social movement perspective remain scarce. This lacuna is not coincidental, but theoretically grounded. According to dominant movement theories, migrants are unlikely subjects of mobilization due to legal obstacles, scarce resources and closed political and discursive opportunities. The article therefore explores how marginalized migrants organize transnational political protest against all evident odds. Drawing from extensive fieldwork and bridging transnational migration and social movement studies, it is argued that migrants mobilize within transnational social spaces, which link relations and emotions acquired on the move with the relational qualities at the locality of arrival. The article illustrates how the transnational spaces most migrants inhabit can be politicized and transformed into particular social formations, for which the term ‘transnational contentious spaces’ is suggested.