Drawing on theoretical frameworks from social movement studies, this article investigates the mobilization of the Ukrainian diaspora in the first 2 years of the full-scale aggression of Russia against Ukraine. Based on desk research and in-depth interviews with activists from Ukrainian organizations in France and Poland, the analysis demonstrates that, despite different political opportunities, the Ukrainian communities reinforced their political position in relation to the institutions of residence countries and gained new spheres of influence in the respective national arenas. Pre-existing mobilizing structures and practices, mostly based on the Euromaidan legacy, facilitated the achievement of far-reaching objectives, the coordination of actions, and the integration of grass-root forms of activism within the community. This was framed by a sense of uniqueness, responsibility to the homeland, and strengthening of national sentiments, a series of factors that sometimes amplified the pressure on newly arrived war migrants. In both countries of residence, the full-scale war led to high levels of diaspora mobilization and consolidation.