Which components of power sharing contribute to the duration of peace and what explains the linkages between institutional design and stability? The authors argue that certain types of political power sharing are associated with more durable peace than others, primarily through their positive effects on governance and public service delivery. In particular, closed-list proportional representation (PR) electoral systems stand out among power-sharing arrangements, due to their ability to deliver superior governance outcomes which, in turn, can promote stability by undercutting the initial motivations for conflict or by reducing the feasibility of rebellion. The authors argue that these positive outcomes result from closed-list PR’s ability to increase party discipline and checks on executive power, while reducing incentives for personalistic voting. The introduction of political institutions in postconflict negotiated settlements allows us to test the independent effects of institutions on governance and stability using survival analysis and a case study.