During the past 45 years, nearly 100 national states have abolished the death penalty for all crimes. This global diffusion poses a puzzle since capital punishment has long been accepted as the ultimate criminal sanction and its abolition has often been politically unpopular in many parts of the world. Although the literature has provided several possible explanations, the role of human rights international non-governmental organizations in worldwide death penalty abolition has not yet received sustained analytic attention. This article offers the first such analysis by arguing that human rights international non-governmental organizations empower pro-abolition constituencies and influence governments toward abolition by framing capital punishment as a human rights violation and lobbying parliamentarians to repeal death penalty laws. Event history analyses of 158 national states from 1967 to 2010 offer strong support for the theory. Controlling for regime type, regional demonstration effects, the Council of Europe, and other rival factors, this article finds that human rights international non-governmental organizations’ local engagement has strongly significant positive relationships with complete abolition. This finding is highly robust against control variable bias, endogeneity bias, omitted variable bias, model dependence, and the alternative operationalization of control variables and the dependent variable. Furthermore, the Philippines example demonstrates the theory’s plausibility. It provides process-tracing evidence that through human rights framing and legislative lobbying, the national sections and member organizations of such human rights international non-governmental organizations as Amnesty International, the International Commission of Catholic Prison Pastoral Care, the International Federation of Human Rights, and Caritas Internationalis led Philippine legislators toward complete abolition in 2006.