Wartime repertoires as institutional blueprints provide a framework for understanding rebel governance and post-conflict state formation, focusing on the SPLM as a political organisation from 1983 to 2023. The central argument is that governance routines created during insurgency become durable organisational repertoires that shape how post-conflict states tax, adjudicate, command, and distribute authority. Drawing on within-case process tracing using SPLM archives, New Sudan Council of Churches documentation, oral histories with Nasir and Torit faction commanders, and ethnographic fieldwork in Juba, Malakal, and Yei, the study engages debates in rebel governance theory, historical institutionalism on path dependence, and Migdal’s “state-in-society” framework. It shows that insurgent governance repertoires are not merely antecedent but constitutive of post-conflict state institutions. Three core claims are advanced. First, SPLM/A wartime practices of taxation, military command, local justice, and movement discipline supplied both personnel and institutional habits to the post-2005 state. Second, personalized command and factional brokerage, while effective for insurgent survival, translated into fragmented chains of accountability once embedded in state institutions. Third, rebel governance legacies can be adaptive when they routinize local service delivery and negotiation, but become pathological when coercive extraction is normalised as a primary technique of rule.