Martin Fertmann explores how Meta's Oversight Board has evolved into a significant actor shaping international human rights standards in online content moderation. Covering Facebook, Instagram, and Threads from 2020 to 2024, the analysis is grounded in the Board's founding documents, 65 decisions, and four advisory opinions. It reconstructs both the Board's self-description and its external perception, tracing its emergence as a source of normative authority within the digital sphere. Using a rule-theoretical approach inspired by H. L. A. Hart's concept of secondary rules, the author examines the Board's internal validation structures and decision-making powers. Complementing this legal-theoretical framework, the study employs the spiral model of human rights socialization from international relations to contextualize the diffusion of human rights norms into private regulation. The findings show that while the Board was initially bound to Meta's internal rules, it increasingly grounds its reasoning in international human rights standards derived from the UN Guiding Principles on Business and Human Rights. This shift establishes a normative hierarchy placing human rights above contractual terms. The study further demonstrates how the Board mediates between Meta, NGOs, and international institutions, gradually narrowing Meta's discretion and institutionalizing human rights within corporate governance. It thereby provides a rigorous contribution to debates on transnational norm formation and digital constitutionalism.