The history of psychology is characterized by unparalleled complexity of its methodology and uniquely ambiguous subject matter closely entangled with issues of power, social justice, and ethics. This complexity requires inordinate levels of reflexivity and conceptual sophistication. In effect, a historian of psychology needs to explicate no less than one’s worldview—a broad position as to how people are situated in the world, relate to, change, and get to know it, and how knowledge develops through time—all coupled with one’s broad sociopolitical ethos. Traditional histories of psychology have operated with an astonishing lack of reflection about these issues. One of many deplorable results is that psychology still grapples with its racist and sexist legacies and lacks awareness of social injustices in existence today. The recently emerging approaches have begun to remedy this situation by focusing on situated practices of knowledge production. This article addresses how human agency can be integrated into these approaches, while focusing on knowledge production as not only situated in context but also, and critically, as a world-forming and history-making process. In tackling the shortcomings of relational approaches including social constructionism, the transformative activist stance approach draws on Marxist philosophy and epistemology—infused with insights from Vygotsky’s psychology and other critical theories of resistance. The core point is that knowledge is achieved in and through collaborative community practices realized by individually unique contributions as these come to embody and enact, in an inseparable blend, both cultural-historical contexts and unique commitments and agency of community members. The acts of being-doing-knowing are non-neutral, transformative processes that produce the world, its history and also people themselves, all realized in the process of taking up the world, rather than passively copying it or coping with it. And since reality is in-the-making by people themselves, knowing is about creating the world and knowing it in the very act of bringing about transformative and creative change. Thus, the historicity and situativity of knowledge are ascertained alongside a focus on its ineluctable fusion with an activist, future-oriented, political-ethical stance. Therefore, the critical challenge for the history of psychology is to understand producers of knowledge in their role of actors in the drama of life (rather than only of ideas), that is, as agents of history- and world-making, while also engaging in self-reflection on the historians’ own role in these processes, in order to practice history in responsive and responsible, that is, activist ways.