Why is the implementation of civil war peace agreements comparatively higher in some countries than in other countries? In this study, I address this puzzle by investigating the effects of insider-outsider leader turnover on the execution of peace agreements. The idea is that leaders should be the fundamental units of analysis to explain the implementation of peace agreements due to more frequent leadership changes than state-level variables, such as the level of democracy, political system, military capability, and GDP per capita. Besides, leader turnover poses a commitment problem in peace processes if outsider leaders differ in their resolve and revise inherited agreements. I test this hypothesis quantitatively using feasible generalized least squares (FGLS) regressions to analyze the panel dataset of this research that covers 34 comprehensive peace agreements of 31 countries from 1989 to 2015. The findings of this study demonstrate the positive impacts of insider leader turnover and the adverse effects of outsider leader turnover on the execution of peace agreements. Hence, whether the implementation of peace agreements will continue depends on who comes to power.