Studies have found that participation in social movements has long-term consequences for individuals’ personal life choices and political beliefs. An important but understudied subject in this literature is the impact of past activism on political behavior in an institutional context. The entry of past activists into Korea’s National Assembly offers a unique opportunity to assess the continuing effects of movement participation in the context of institutional politics. Analyzing roll call data related to Korea’s participation in the Iraq War, we explore the relative effects of movement participation and institutional pressure after accounting for legislators’ current ideological positions. Results from regression analyses show that while party and ideology remain strong predictors of voting behavior, past participation in social movements continues to influence political action. This study extends the scope of research on the consequences of social movements by pointing to the impact of movement participation on political behavior in an institutional setting.