This article analyzes the increasingly prominent role of regional organizations (ROs) and non‐governmental organizations (NGOs) in promoting norms in mediation processes. In particular, we seek to understand the processes by which RO and NGO mediators promote the inclusivity norm to negotiating parties and the outcomes that result. We employ the concepts of local agency and social practices in examining the normative agency of ROs and NGOs in promoting and redefining the inclusivity norm. Through illustrative case studies of peace processes in South Sudan and Myanmar, we argue that ROs’ and NGOs’ mediation practices reflect their claims to alternative resources of power, such as long‐standing expertise and insider status in the context, and build congruence with strong local norms. We provide nuanced theoretical insights on RO and NGO mediators’ claims to agency and provide empirical illustrations on how these claims contribute to constitutive changes to norms.
