The academic literature on unethical leadership is witnessing an upward trend, perhaps given the magnitude of unethical conduct in organisations, which is manifested in increasing corporate fraud and scandals in the contemporary business landscape. Despite a recent increase, scholarly interest in this area has, by and large, remained scant due to the proliferation of concepts that are often and mistakenly considered interchangeable. Nevertheless, scholarly investigation in this field of inquiry has picked up the pace, which warrants a critical appraisal of the extant research on unethical leadership. To this end, the current study systematically reviews the existing body of work on unethical leadership and offers a robust and multi-level understanding of the academic developments in this field. We organised the studies according to various themes focused on antecedents, outcomes and boundary conditions. In addition, we advance a multi-level conceptualisation of unethical leadership, which incorporates macro, meso and micro perspectives and, thus, provide a nuanced understanding of this phenomenon. The study also explicates critical knowledge gaps in the literature that could broaden the horizon of unethical leadership research. On the basis of these knowledge gaps, we develop potential research models that are well grounded in theory and capture the genesis of unethical leadership under our multi-level framework. Scholars and practitioners will find this study useful in understanding the occurrence, consequences and potential strategies to circumvent the negative effects of unethical leadership.