This paper asks what are the potential responsibilities to respect, protect, and fulfill international human rights law (IHRL) of a particular class of non-State actors: non-governmental organizations (NGOs). The paper focuses on those NGOs pursuing development in a post-genocide/post-mass-atrocity transitional justice context acting simultaneously in partnership with State governments, as proxies, and providing essential public goods as part of their development remit. It uses post-genocide Rwanda as an example to illustrate how respect and fulfillment of the IHRL pertaining to reparative justice are hindered by failing to hold NGOs responsible for IHRL. This paper defines reparative justice in accordance with the UN Basic Principles and Guidelines on the Right to a Remedy and Reparation for Victims of Gross Violations of IHRL and Serious Violations of International Humanitarian Law. These are centered upon five principles: restitution, compensation, rehabilitation, satisfaction, and guarantees of non-repetition. I argue that many development NGOs in Rwanda, by not adequately incorporating reparative justice into their development and transitional justice remit and not acknowledging and responding to the distinctive rights and vulnerabilities of genocide survivors, are neglecting IHRL on the right to reparative justice. They have the capacity to prioritize reparative justice in their programming for genocide survivors and in their negotiations with the Rwandan government of how development aid will be disbursed in Rwanda, who will be its recipients, and the prioritization of those facing disadvantage so as not to further marginalize them. I argue, furthermore, that current soft law demands that NGOs should never enter into a contract for provision of development aid with a sovereign that knowingly entails – whether by commission or omission – a violation of IHRL. Though States are ultimately held legally responsible for the acts of NGOs this should not prejudice NGOs being held socially and morally responsible in some capacity and some degree, simultaneously. There is potential for new soft-law moral and social standards regulating NGO behavior to become legal obligations, if they eventually achieve widespread status and practice as customary international law.