This article examines the conceptual interconnectedness of the federal mandatory immigration detention regime and mandatory minimum sentencing in Western Australia, two procedural and political responses to populist concerns regarding ‘waves of boat people’ and ‘waves of crime’. Through a comparative analysis, the ‘mandatory’ character of these ostensibly separate and distinct practices is shown to limit judicial discretion and oversight of government action. Mandatory practices privilege goals of deterrence, incapacitation and retribution and depict these as promoting the best interests of national safety and security. These practices are also markedly similar in the sense that they are at odds with the principle of due process, unfairly tipping the balance away from individual freedoms and towards the interests of the state, offending aspirational notions of judicial function, the rule of law and natural justice.