This article evaluates the extent to which Michel Foucault’s concepts of sovereignty and biopolitics satisfactorily explain the UK’s law and practice of denationalising terrorists. It argues that the ancient Foucauldian sovereignty has re-emerged in terms of the process of the expansion and exercise of the Home Secretary’s denationalisation powers, with the Home Secretary accorded broad discretion to decide whether to use this exceptional measure and, importantly, whether to normalise the exceptional. Yet Foucauldian sovereignty cannot be said to have re-emerged in terms of the outcome faced by the denationalised terrorist who is largely not sent to political death or rendered bare life. Denationalisation is justified to the citizens as a necessary security measure for the protection of society as a whole. The terrorist is effectively characterised as an enemy and threat to security because security is increasingly informed by what executive officials deem to be the society’s values, and participation in terrorist activity conflicts with those values. As such, while it is contentious whether denationalisation constitutes Foucauldian sovereignty, the ends of denationalisation are biopolitical.