ABSTRACT This article assesses the agency of UN mediators through a single case-study of the UN mediator in Syria – Staffan de Mistura. Drawing on and contributing to an emerging research agenda, we argue that UN mediators do have significant room of manoeuvre and thus the ability to conceive, negotiate, and execute key mediation policy-decisions. Our analysis bridges the literature on levels of analysis in International Relations (IR) and Foreign Policy Analysis (FPA). We developed a method that uses process-tracing to identify distinct mediation initiatives. We then pinpoint the mediator’s input on the conceptual and operational components of these main pillars of the mediation process. We question the prevailing perspective wherein the individual mediator has become conspicuous by their absence as the research gaze has been geared towards contextual constraints to mediation, the organization employing the mediator, and developing generic guides for good practice in ‘successful’ mediation. We put the study of the mediator’s agency firmly back into the comparative study of mediation, this way strengthening the validity of arguments that mediators’ personalities, skills and their individual characteristics shape their mediation initiatives just as they point up to considerable personal responsibility for which they need to be better held to account.