The parallels and differences between current forms of populism and early 20th-century fascism have been the focus for much discussion. This article examines the relevance today of Karl Mannheim’s analysis of fascism and of its relationship to democracy in the 1930s. He argued that the threat of fascism arose from the very nature of liberal democratic society, rather than being a product of external forces. He claimed that liberal democracy is transitional, rather than stable in character, and that the new emerging form of governance that was required to replace it shared a key component with fascism: a high level of social and economic planning. At the same time, he insisted that, as a pathological development, fascism served to illustrate the disastrous consequences that a failure to engage realistically with the process of societal development can have for upholding Western civilisational ideals. This article explores Mannheim’s arguments against the background of current thinking about populism and ‘post-democracy’.