Antifascists have developed action-oriented principles and practices for collective resistance to fascism. In this article, we discuss antifascism as "praxis," which is the nexus of theory and practice through collective reflection and action. Antifascist praxis can inform developmental science at individual and contextual levels of analysis. For the study of individual developmental trajectories, we examine how antifascist praxis can inform research to stop fascist recruitment of youth and counter-recruit youth into liberation movements. For the study of developmental contexts, we use the example of family separation to examine how antifascist praxis can inform research to identify fascist threats and support collective action against fascist violence. We also present next steps for developing a field of scholarship in which communities of developmental scientists engage in antifascist praxis. As developmental scientists, we must see ourselves as part of - not objectively disconnected from - broader mass movements building power against fascism and pursuing liberation for all.