Democratic citizens confront a range of problems framed as “security” issues, in policy areas such as counterterrorism and migration control, which place substantial political pressure on democratic norms. We develop a normative theoretical framework for assessing whether and how policies that curtail democratic governance standards in the name of security can be justified as politically legitimate. To do so, we articulate a novel normative account of legitimacy, which integrates insights from both democratic and realist traditions of thought to illuminate the complementary contributions of democratic and security standards to political legitimacy. We further elaborate a framework for applying this theoretical account to political practice in the form of a policy-focused “security test” for legitimacy in democratic states. Finally, we explore how this test may be deployed to help resolve policy dilemmas in democratic practice, by examining its application to a case study of national policy on irregular boat arrivals in Australia and Canada. Through this analysis, we contribute to the development of both richer theoretical understandings of the complex modern value of political legitimacy, and clearer action-guiding principles for balancing competing demands of legitimacy within securitized democratic policy regimes.