SignificanceMacrophage–myofibroblast transition (MMT) is a newly discovered pathogenic process by which TGF-β1/Smad3 signaling promotes tissue scarring. However, systemic targeting of Smad3 may impair host T cell immunity; therefore, it is preferable to focus on downstream mechanisms to identify antifibrotic therapies that avoid targeting Smad3 per se. In this study, we revealed a brain-specific transcription factor Pou4f1 as the key regulator by which TGF-β1/Smad3 signaling executes MMT. Macrophage-specific silencing of Pou4f1 effectively blocked progression of renal fibrosis in two mouse kidney disease models. Thus, Pou4f1 represents a therapeutic target in MMT-driven renal diseases.