How does the self-relevance of a social movement shape individuals’ engagement with it? We examined the decision-making processes that underlie support for Black Lives Matter (BLM) among Black, Hispanic, Asian, and White Americans. We find significant between-group differences in levels of support for BLM, both in terms of past behavior (Study 1) and in terms of future intentions to support the movement (Study 2). These differences notwithstanding, thinking about how one’s decisions impact others – which we label impact mindset – explains support for BLM across racial groups, cross-sectionally as well as longitudinally (over eight months later). Our findings underscore the equivalence of the impact mindset construct across racial groups and its predictive power in the context of BLM. We conclude that, although the struggle for racial justice has different meanings for different racial groups, the same mindset underlies both in-group advocacy and allyship in the context of BLM.