The thesis of the ontological primacy of antagonism, thus the political, is central to Chantal Mouffe’s call for taming antagonism into agonism, or agonistic pluralism. Within planning theory, Mouffe’s conflictual ontology that underpins this call has raised questions over the ontological assumption of the presently prominent and consensus-oriented communicative and deliberative planning approaches. This is because these approaches consider consensus formation as a normative ideal and always at least a potential outcome from open and inclusive deliberation, that is, ontological. Yet, the notion that antagonism is also an ever-present possibility for all social relations and therefore an ineradicable risk for consensus-building effort in planning practices appears to be increasingly accepted even by communicative planning theorists. In this article, I trace the origin of Mouffe’s thesis of the ontological primacy of antagonism back to both her original collaborative work with Earnest Laclau, Hegemony and Socialist Strategy, and Carl Schmitt. With Derrida and Laclau, I then argue that this Mouffean thesis does not hold: antagonism operates at the ontic level in the social and it is only but one way of discursively inscribing the experience of exclusion and the use of power. This insight supports a new, post-antagonism approach to politics and the political based on the ontology of radical negativity. Finally, I discuss how this approach can be linked with planning theory by adopting a de-ontologised notion of the political. I conclude by arguing that since agonism is not the only option for dealing with antagonism for the socially established actors, for example, planners, its implementation in planning practice can appear merely as a top-down imposition of a democratic ethos. Sometimes, depoliticisation of agonistic planning might therefore be necessary.