Legitimacy, this contribution argues, plays a key role in connecting transitional justice mechanisms to sustainable peace, and strengthening people’s perceptions of legitimacy should be of concern to all those involved in these institutions. Here, it is important to take an empirical, people-based approach to legitimacy, with regard for its dynamic quality. This approach should focus on all three dimensions of legitimacy: the input into transitional justice mechanisms, the popular adherence to the demos that sets them up, and their output. In addition, legitimacy requires an explicit deliberation by means of justificatory discourse, and the involvement of all stakeholders. Drawing on the example of Rwanda’s multi-layered justice mechanisms this model then draws attention through the processes through which various internal and external actors can seek to (de)legitimate transitional justice institutions, and what this entails for the legitimacy of these mechanisms in general.