Historiography on the emergence of the Human Right to Health (HRH) and the positive definition of health in the World Health Organization (WHO) Constitution has largely traced their roots to social medicine. This article complements that view by examining the genealogy of both through the influence of Mental Hygiene (MH) and its entanglement with eugenics. The conceptual framework interweaves Michel Foucault's and Giorgio Agamben's perspectives on the convergence of sovereignty and biopolitics. The analysis covers developments from the early to mid-20th century, including the rise of MH and its key innovations and displacements, such as the individual–environment adjustment matrix, its eugenic connections, and the emergence and shifts of child guidance and the interdisciplinary turn. These trajectories are shown to converge in the WHO's constitutional process through Brock Chisholm's biopolitical project to produce an apolitical, well-adjusted, efficient, and fully pacified “world citizen”—an ideal he embedded in the HRH and promoted as the Constitution's final drafter and the organisation's first director-general. The article concludes that the HRH represents both a landmark in the pursuit of social justice within the welfare-state matrix and a product of dis/ableist and sanist technocratic rationality that must be recognised and urgently redressed.