During the past three decades, national human rights institutions (NHRIs) have become an increasingly common feature of transitional justice frameworks. Promoted by international organisations, including the United Nations and its relevant agencies, and by several regional NHRI networks, contemporary human rights policy and discourse has coalesced around the idea that NHRIs may contribute to transitional justice by ensuring accountability and combatting impunity. In practice, however, relatively little is known about the specific roles envisaged for and played by NHRIs in transitional and post-conflict contexts. This article examines the role of NHRIs in transitional justice from the 1970s to the present. Drawing on the mandates and experiences of 137 NHRIs, it demonstrates that NHRIs are increasingly being afforded responsibility for three types of accountability tasks associated with transitional justice: investigating past human rights violations, holding post-transitional actors and institutions to account; and managing the provision of reparations to victims of human rights abuses. This, it argues, represents a small but significant development, both for the practice of transitional justice and for the roles and functions of NHRIs.