A transnational legal order (TLO) authoritatively shapes “the understanding and practice of law” in a specific area of social activity, involving both state and civil society actors, and linking national, regional, and international levels. We argue that a TLO has emerged and settled since 1945 around capital punishment. Our analysis of the death penalty TLO treats “bottom-up” and “top-down” effects as interconnected, addresses the creation of legal order at both national and international levels, and emphasizes the recursivity linking developments at both levels. We trace the development of death penalty abolition from its origins in the immediate aftermath of World War II. Because the practical effects of abolition—in shaping legal and penal practice—necessarily occur at the national level, the analysis focuses on the international, transnational, and domestic factors that lead states to end capital punishment. After describing the emergence of a TLO abolishing the death penalty, we offer a new way of measuring the global and country-specific activities of transnational advocacy groups (Human Rights Watch and Amnesty International). We incorporate that measure in an analysis of data from about 150 countries. The central hypothesis is that making the TLO on capital punishment effective through abolition in national law requires modes of political action that overcome majoritarian public support for retention. We suggest two domestic institutional features that make abolition more likely despite retentionist popular opinion: proportional representation in the legislature and independent courts. We also suggest that transnational non-governmental organizations (NGO) and some regional organizations can support the move to abolish. The data analysis is largely consistent with these propositions and brief case studies illustrate the principal mechanisms.