Cognitive radicalization remains an issue for communities battling terrorism. Recent empirical investigations into the psycho-social processes involved with radicalization have revealed social exclusion, cognitive inflexibility, and perceived threats to an ingroup as significant predictors for one’s propensity to engage with radical content and commit to offline behaviors. This study investigates the utility of user engagement and the proxy effect on cognitive radicalization by examining users’ engagement with a radical-right online ecosystem. The study supported the assumption that content featuring outgroup prejudice would affect the cognitive radicalization process. Several results demonstrate the importance of user engagement in the process of radicalization. In this analysis, they support an engagement-dependent framework where individual posts carry higher radicalization likelihoods based on the amount of user engagement they receive. These findings have an implication for future research into a user’s behavioral trajectories, from viewing and engaging with content to joining a radical group or committing offline violence against their communities and perceived outgroups.