Eco-anxiety has emerged as a significant psychological response to the climate crisis. Yet its relationship with pro-environmental behavior remains far from settled, with findings ranging from behavioral paralysis to active engagement and seemingly contradictory evidence accumulating across studies. To clarify both the magnitude of this association and the conditions under which it holds, we conducted a systematic review and three-level random-effects meta-analysis. We systematically searched five databases (ProQuest, APA PsycArticles, PubMed, among others) through April 2025, identifying 20 independent studies that contributed 60 effect sizes (N = 34,206). The pooled results revealed a significant, small-to-moderate positive association between eco-anxiety and pro-environmental behavior (r = 0.24, 95% CI [0.15, 0.32], p < 0.001). So far, fairly straightforward. The complication emerged when examining heterogeneity: we observed substantial variation across studies (I² = 95.4%), with a 95% prediction interval ranging from −0.22 to 0.61. What this tells us is that eco-anxiety does not uniformly predict action across contexts; the variability is considerable and meaningful. Moderator analyses offered important clarification. The association proved significantly stronger for public and collective behaviors, such as activism and advocacy (r = 0.36), compared to private sphere actions (r = 0.22). Beyond this, effects were more robust in adult samples (r = 0.30) than among adolescents (r = 0.18). These findings suggest something worth emphasizing: eco-anxiety appears to function not merely as a pathological burden but as an adaptive, context-sensitive correlate of collective engagement. Put differently, the distress people experience in response to climate change may channel productively into systemic action, particularly when social and collective pathways are available. What this means for practice is significant. Future interventions, in this perspective, should focus on channeling climate distress toward collective, structural engagement rather than defaulting to individual behavioral prescriptions alone.