As the urgency of the climate crisis grows, increasing numbers of people are joining collective efforts to protect the environment. Yet, those dedicated to this cause often face numerous stressors that can accumulate to activist burnout. This article presents a quantitative examination of activist burnout among environmentally engaged individuals. Drawing on two cross-sectional studies (N = 268, N = 483), we show that more extensive involvement (measured by hours spent on engagement) and being paid for engagement were positively associated with activist burnout. In contrast, social identification and personal self-efficacy were negatively related to burnout. Our research further explored a range of other health-related variables, laying a foundation for this emerging field. We discuss our findings in the light of strategies for fostering resilience within environmental movements.