Young people will experience stronger consequences of climate change in their future adult lives than older people are facing today. Against this background, large demonstrations and school strikes for climate protection started all over the globe, called the Fridays For Future (FFF) movement. Drawing on the social identity model of pro-environmental action (SIMPEA) and theories on pro-environmental actions of children and adolescents, we examined psychological drivers of pro-environmental activism in the FFF movement. Young people recruited during a FFF demonstration in a German city (N = 144, 16–25 years old) and from all over Germany recruited through an online panel (N = 418, 13–25 years old) participated in our online survey study. A comparison of these samples and a regression analysis with the joint sample both revealed that perceiving friends participating in the movement, identification with others engaging in climate protection, and personal norms in the form of a felt obligation based on values were most strongly related to their participation in FFF protests. We discuss theoretical implications of our findings as well as practical implications for interventions to encourage young people's pro-environmental engagement.