Legal scholarship has not addressed whether the persistent objector rule applies to general principles of law (GPLs). This article is the first to examine both theoretical and practical incompatibilities between the persistent objector rule and GPLs. It traces the brief history of the persistent objector rule and how it was raised in the International Law Commission (ILC) and the United Nations Sixth Committee (Legal), sparking debate over its applicability. Following the ILC’s omission of a Draft Conclusion on the persistent objector rule in its work on GPLs, this article examines its theoretical and practical implications, noting its incompatibility with: (i) GPLs derived from domestic legal systems; (ii) internationally-derived GPLs; and (iii) regional or subregional GPLs applied beyond the region in which they originate. The analysis combines theoretical, conceptual and practical reasoning supported by evidence from State practice, jurisprudence and scholarship. It concludes that the persistent objector rule is incompatible with GPLs emerging from domestic or international legal systems. Furthermore, it argues that States’ objections to the application of regional or subregional GPLs within subject-specific legal orders or autonomous regional or subregional legal systems do not pertain to the persistent objector rule as such. Rather, they concern the appropriateness of incorporating these norms into another regional or subregional legal system.