The importance of health for social justice has increased since the end of the 20th century, particularly following the recognition in the 1995 Copenhagen Declaration that "people are entitled to a healthy and productive life in harmony with the environment." However, a majority of people worldwide still do not enjoy good health. Numerous efforts have been made by the international community to address this situation in line with the principles of equity and social justice. The agenda 2030 serves as a remarkable example of these efforts, positioning health at the centre of the program, acknowledging the existence of social determinants of health, and affirming the necessity to tackle the causes of health inequities and attend to the needs of disadvantaged groups. Individuals with rare diseases face specific risks and challenges primarily due to unmet health needs stemming from a lack of research and development of suitable medical technologies. In this article, we explore the reasons explaining the injustices faced by these patients, as well as ways in which a human rights-based approach to people with rare diseases can provide arguments in favour of States' action. By considering the right to science as a complementary right to the right to health, we argue that States must promote the science for treating rare diseases and render applications of science accessible and affordable, thereby contributing to the realisation of a just and equitable society.