This paper develops a materialist and performative conception of power, proposing a theoretical framework that bridges Barad’s intra-active agential ontology and Foucault’s microphysics of power. The article uses empirical data collected from a social clinic in Greece where the traditional apparatus of the clinic is contested and experimentally reconfigured. We focus on three overlapping themes and reflect on how power relations materialize themselves through everyday practices and multiple entanglements between human and non-human agents. We argue that these entanglements constitute the dynamic matter of power: their performative reiteration determines how power matters. By showing how power materially exceeds the manifest intentions of human agents, our case study aims to contribute to an idea of alternative organising that accounts for the materiality of mundane posthuman entanglements within an antagonistic understanding of power.