<p>Contingent academic employment has become a salient feature of many higher education systems over recent decades. At the same time, there remains limited understanding of how such employment has come to be institutionalised—that is, framed and accepted as a legitimate feature of the contemporary university within specific national settings. Bringing the conceptual resources of institutional theory to bear on the case of the Australian higher education system, this paper offers a conceptual account of the key institutional forces that have contributed to the legitimisation of contingent or “casual” academic employment within that system. Building upon the conceptual lens provided by Scott’s theory of institutional pillars, our account spans the key institutional domains of national employment legislation, national higher education policy, university management and the academic profession. According to our conceptual account, the legitimisation of casual academic employment in Australia has no single cause but has been driven by a complex interplay of, in parts, mutually reinforcing regulative, normative and cultural–cognitive institutional dynamics. One implication arising from this is that responsibility for legitimising casual academic employment is best conceived of as distributed, with various collective actors, to varying degrees and at times unintentionally, all having contributed.</p>