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Objectives The current study seeks to explain changes in support for violent extremism during the transition to early adulthood. This period during the life course could increase uncertainty and vulnerability to radicalization, or alternatively lead to maturation, prosocial bonds, and consequently less support for violent extremism. In the absence of population-based longitudinal data on violent extremist attitudes, we know very little about how and why attitudes change during this period. Method Data came from an ongoing longitudinal cohort study in Zürich, Switzerland (n = 910). First, we assessed the variation in violent extremist attitudes between ages 17 and 20 using the Reliable Change Index. Second, we used hybrid regression techniques to investigate to what extent theoretically relevant factors can explain between- and within-individual differences in violent extremist attitudes. Results Our results show that violent extremist attitudes are largely stable or declining between late adolescence and early adulthood, and that within-individual changes in low self-control, conflict coping skills, and peer disapproval of violence can in part explain these changes. Conclusions For young people in Zürich, the transition to early adulthood was characterized by increases in psychosocial maturity, more prosocial peers, and less deviant behavior, which in turn was associated with lower support for violent extremism. Existing research on effective interventions for criminal desistance and disengagement from gangs may therefore be fruitful avenues for developing programs aimed at reducing support for violent extremism and fostering deradicalization.