Why do some civil wars end sooner than others? Extant theory focuses on how exogenous factors, such as resources or third parties, exacerbate the commitment problem faced by belligerents. In explaining the duration of civil war, we focus on factors endogenous to the disputing parties. We advance a theory suggesting that the tenure of a state’s leader influences war duration. Specifically, we argue that longer-tenured leaders tend to fight longer civil wars. This is because long-tenured leaders have a more predictable policy reputation. Based on this predictable reputation, opposition groups have decided to fight the leader rather than bargain peacefully. Therefore, they will be unlikely to believe any policy concessions the leader might offer. This commitment problem looms larger for leaders who do not have domestic institutions that can credibly commit the leader to policy changes. We find robust statistical support for our conjecture. The findings have important implications for leader-centric studies of conflict, as well as for our understanding of bargaining during war.