The long-term electoral viability of rebel parties depends, in part, on acceptance of them as legitimate political actors. Yet civilians often punish perpetrators of past violence at the ballot box and conflict generates long-term antipathies that can impede democratic integration of former rebels. This paper offers a theoretical conceptualization of rebel party stigmatization and uses an experimental approach in Colombia, informed by interviews on the ground, to clarify the conditions under which stigmatization can be a relevant barrier for rebel parties. First, in semi-structured interviews, rebel party leaders and members uniformly claim that civilian stigmatization of the party is pervasive. Second, we design an endorsement experiment to measure rebel party stigmatization, whether the penalty is distinct from assessments based on ideology or platform, and for whom stigma is strongest. Civilians penalize policies and statements endorsed by the rebel party even when compared to endorsement by ideologically similar parties, indicative of stigmatization. Such rebel party stigmatization is especially strong among two types of citizens. First, citizens who otherwise share a similar ideology with the rebel party but rejected violence are the most stigmatizing, due to a political victimization effect. Second, citizens who did not live in communities with substantial FARC governance and presence are more stigmatizing—those who lived in rebelocracies do not penalize rebel parties but also do not support them strongly.