Antigovernment milieus (AGM) have become increasingly prominent in the contemporary Australian security environment. Recent high-profile events such as the shootings in Porepunkah, arson at Old Australian Parliament House, and the counter-terrorism disruption of an anti-government coup plot, underscore the need to understand anti-government. The purpose of this article is to develop insight into the general ideological contours of anti-government beliefs in Australia. It achieves this through a discourse analysis of international knowledge contexts, which resulted in the 3I Framework, organising the core ideological categories of Illegitimacy, Individualism, and Immunity. We then applied this to Australian case studies to illuminate localised narratives and beliefs. To orientate this in theory, we argue that Australian anti-government ideologies are ‘thin-centred’, focused on political legitimacy, and often lacking a coherent theory for social change.