A sizeable literature has argued that Islamist movements perform better than their non-Islamist rivals in elections and service provision, or in survival under repression due to their reputation, organizational structure, ideology, and economic policies. However, this “Islamist advantage” has mostly been analyzed in non-war settings and only relatively recently been probed in the context of armed conflict. Here, the focus has been on the comparative advantage of extremist Islamist groups in relation to more moderate (Islamic) actors, not on Islamist groups among each other. However, both comparisons are necessary in order to get a fuller understanding of what an Islamist advantage means in wartime. Specifically, I argue that both a group’s organizational structure and ideology needs to be taken into account. I demonstrate this by looking at the case of the armed Islamist group Ahrar al-Sham in the Syrian civil war which was founded with strong Salafi-jihadist credentials and both ideological and personal connections to international jihadist networks. It quickly became one of the most influential groups in Syria. In contrast to other Islamist actors, the group went through an unprecedented process of change and approximated more moderate groups in its public discourse. However, Ahrar al-Sham was also one of the most important ‘practical’ allies of the notorious jihadist groups ISIS and Jabhat al-Nusra, and remained divided over which course it should prioritize. These contradictions and internal divisions had a negative impact on both its ideological coherence and its ability to build a centralized organization. This had fatal consequences eventually not only for the group, but also for the insurgency as a whole in terms of losing one of the most crucial actors who could have negotiated on behalf of the (armed) Syrian opposition. Based on interviews with members and leaders of Ahrar al-Sham and other Syrian rebel groups, as well as an analysis of primary documents released by the group, I theorize what an Islamist (dis)advantage means in conflict settings characterized by intra-Islamist competition.