Law following and law breaking are often conceptualised as polar opposites. However, authorities in liberal democracies increasingly deploy a strategy of what I call plausible legality in order to secure immunity and legitimacy for proscribed practices. Rather than ignore or suspend law, they construct legal justifications for human rights abuses and other dubious policies, obscuring the distinction between legal compliance and non-compliance. I argue this is possible because instabilities in legal rules make them vulnerable to manipulation and exploitation. By tracing American rationales for contentious ‘enhanced interrogation techniques’, indefinite detention, and ‘targeted killing’ practices in the ‘Global War on Terror’, I show that law need not always be abandoned or radically reconstituted to achieve troubling ends and that rule structures enable certain patterns of violation while limiting others. The international prohibition on torture is robust and universal, but provides vague definitions open to interpretation. Detention and lethal targeting regulations are jurisdictionally layered and contextually complex, creating loopholes and gaps. The article concludes by reflecting on implications for the protection of human rights. While law is not wholly indeterminate, human rights advocates must constantly advocate shared legal understandings that constrain state violence.