The study of mediation in resolving armed conflicts remains a promising area of research in international relations. However, contemporary IR research provides a limited understanding of the role of the mediator’s military power in the cessation of hostilities and the implementation of peace agreements. We have suggested that asymmetry and parity can characterize the military superiority (or lack thereof) of a mediator state. To assess the relevant characteristics of military power, we propose using a generalized indicator of military asymmetry created through a simple comparative analysis. Within the framework of the methodology presented in this article, various metrics of the military power of the parties to conflicts and their respective mediators were compared in pairs with each other according to the criterion of threshold values (quartiles), indicating an asymmetry (or parity) of military power. Various thresholds of sufficient skewness, ranging from 20% to 50%, were then also used to aggregate the binary scores into a single score. Through the assessment of a series of regression models, we were able to establish that the aggregate military superiority of the mediator state over the warring parties contributes in a statistically significant manner to both the immediate cessation of hostilities and the successful establishment of peace in the long term. Control variables in the form of the features of peace agreements also influence the positive outcome of the peace process. Key among these are increasing the transparency of political decision-making procedures and the involvement of various social groups in power processes at various levels. The results of this study demonstrate the interconnectedness of military force and successful mediation and also indicate the complementarity of military and negotiation components in the context of state-led mediation. Thus, this study proposes to transform the idea of mediation that currently dominates international relations theory.