--- - |2 This study aimed to further the understanding of the processes involved in activism, as a form of collective action, based on differences in the quality of moral judgment and political ideology. It began with the assumption that differences in the quality of moral judgment can lead individuals to engage in different forms of collective action: activism or radicalism. Therefore, the associations among the variables political ideology, social identity, perception of social justice, activist identity and commitment, personal political salience, perception of efficacy and life purpose were analyzed. Path modelling was used to construct two models of political action: one based on conventional moral judgment and conservative political ideology, and the other based on post‐conventional moral judgment and egalitarian political ideology. These two models were tested on samples of Brazilian and Spanish youths. The results confirmed the validity of using developmental social psychology to understand activism as a form of political action. The results confirmed the central hypothesis that differences in the quality of moral judgment and in political ideology are related to willingness to engage in qualitatively different types of actions: young people with conventional moral judgment and conservative political ideology declared their intention to engage in activism, while young people with post‐conventional moral judgment egalitarian political ideology reported the intention to engage in both activist and radical actions. - Scandinavian Journal of Psychology, EarlyView.