Foucault's inspiration from Nietzsche in terms of writing critical histories is difficult to overestimate. However, this article advances an interpretation of Foucault's approach to history which focuses on another, less readily evident, dialogue partner, namely the Marxist tradition and, more precisely, French Maoism. The first part of the article details Foucault's involvement in the Maoist-inspired activist group, Groupe d'information sur les prisons (GIP). It is argued that Foucault's practical experience from GIP left crucial marks on his contemporaneous statements on the genealogical method and his critique of “totalizing institutions,” “uniform discourse” and “juridical universality.” The second part of the article offers a close reading of Foucault's reflections on genealogy in his 1976 lecture series which demonstrates how the Maoist activist principles noticeably resonate in these statements. The aim of the article is threefold. First, to bring attention to largely neglected sources of inspiration for Foucault's genealogical approach, which complement those represented by Nietzsche. Second, it seeks to obtain a better understanding of Foucault's relationship to Marxism, a relationship often portrayed as unambiguously negative. And third, the goal is to demonstrate how principles developed in Maoist political activism are not only realized in Foucault's activities within the GIP, but also in his lecture-hall formulations of genealogy, power, and critique.