Existing research demonstrates that strong civilian control reduces the risk of civil war recurrence in post-conflict societies. However, little is known about the factors that erode civilian control after conflicts end. This paper argues that governments in post-conflict societies that form new militias to manage domestic opposition experience a weakening of civilian control. Specifically, two causal mechanisms explain how the creation of militias contributes to the decline of civilian authority. First, while post-conflict civilian governments often establish militias to lessen their dependence on the military, this strategy paradoxically strengthens the military’s inclination to challenge civilian authority. Second, the use of militias against domestic opposition undermines the government’s legitimacy, creating vulnerabilities that the military can exploit to further weaken civilian control. I test these arguments using data on pro-government militias (PGMs) formed after the conclusion of civil wars between 1981 and 2014. The findings reveal robust statistical support for these claims, and the results hold across a variety of model specifications, providing strong evidence for the negative effects of militias on civilian control in post-conflict settings.