The World Health Organization (WHO) has been shaped by global health law throughout its history. Drawing from the post-war establishment of global governance under the United Nations (UN), the modern foundations of global health law were laid by the WHO Constitution, which provided WHO with a range of normative authorities to realize its mandate as the UN’s directing and coordinating authority in global health. Yet WHO has faced political challenges in exercising these normative authorities to advance global health law, revealing the limitations of law as a foundation of global health governance. This article chronicles the 75-year evolution of global health law through WHO governance – beginning in the expansive authorities under the WHO Constitution, examining the political obstacles that long hobbled legal advancements, recognizing the revitalized space for law and policy in the twenty-first century, and analyzing the new limitations exposed by the COVID-19 pandemic response. Global health law reforms will be essential to strengthen global health governance. By analyzing how past challenges to global health law offer lessons for ongoing legal developments, this timely historical analysis offers lessons for WHO reforms to facilitate global solidarity.