Informal networks persist after conflict and undermine liberal peace-building. While these adverse effects are well-known, how informal networks survive beyond conflict is less understood. Scholars explain informal networks’ persistence by their stability and cohesion, attributed to solidarity of ascriptive bonds such as ethnic ties. In these accounts, networks are approached as actors and not as relational structures. We address this gap in the peace-building scholarship and conduct a longitudinal study of relations within an informal network in Bosnia and Herzegovina. Drawing on the political approach to networks, and applying Social Network Analysis, we investigate actors’ relational power and reveal how network actors use their connections to create strategic coalitions and opportunistic collaborations enabling them to exploit different stages of the peace-building process. We demonstrate that unequal distribution of relational power creates vested interests in sustaining the network and in seeking access to it, and how dynamic reconstitution of relational power within the network ensures continuity of network action from war to peace. From a policy perspective, this structural account of informal network persistence suggests a need for a better understanding of the dynamics among co-ethnics within an informal network that allows network members to subvert efforts to counter informality and undermines post-conflict institution-building.