This paper aims to identify and compare how international law has been mobilized to fill domestic rule of law gaps regarding the individual accountability for gross human rights violations in post-authoritarian transitions in Argentina, Brazil, and Chile. Mapping how courts —especially supreme courts— mobilize historical narratives to deal with the past, it argues that not only the institutional architecture but also its combination with a substantive historical understanding of the nature of the previous regime is important for accountability to happen. It explores the argument that in the aftermath of authoritarian rule, broader social support of the former regime influences judicial historical interpretation in favor of continuity between the authoritarian and democratic legal orders (promoting a sense of authoritarian legality adequacy). In the opposite way, broader knowledge of human rights violations and political pressure for accountability tend to decrease social support for authoritarian provisions, stimulating a perception of legal inadequacy that makes rule of law gaps explicit, which favors the use of international law as a subsidiary source that provides formal and legitimate legal criteria to address past wrongdoing. The wider the recognition of authoritarian rule as an unlawful regime, the better the chances that a global norm of individual accountability will make its way into domestic courts.