<p>Neuropsychiatric disorders represent a diverse range of conditions, such as schizophrenia, major depressive disorder (MDD), anxiety, post-traumatic stress disorder (PTSD), and obsessive–compulsive disorder (OCD), with shared immunological and neuroinflammatory signatures. The key immunomodulatory role of forkhead box P3 (FoxP3), the master transcription factor for developing and maintaining regulatory T cells (Tregs), has been highlighted in recent research in central nervous system (CNS) diseases. This review integrates evidence of FoxP3 expression and dysregulation correlating with the development and evolution of neuropsychiatric disorders. We discuss FoxP3’s molecular architecture, physiological roles, and its growing role in controlling neuroinflammation and immune homeostasis. We discuss further the complex network of signaling pathways—JAK-STAT, IL-2/STAT5, TGF-β/SMAD, PI3K/Akt/mTOR, AMPK, NF-κB, and Notch—controlling or controlled by FoxP3 based on both preclinical and clinical evidence. It is suggested by research that modulation of these pathways impairs FoxP3 expression and Treg function, thus modifying neuroimmune homeostasis and neuropsychiatric outcome. The interaction of FoxP3 with STAT5 or SMAD3, for example, increases the suppressive potential of Treg, whereas PI3K/Akt or Notch signaling–dependent suppression of FoxP3 helps in immune deregulation. Inclusion of FoxP3 into the neuroimmune model provides an attractive paradigm through which to consider and therapeutically address immune dysfunction in neuropsychiatric illnesses. This review identifies FoxP3 as a likely biomarker and therapeutic target, opening the way for novel immunomodulatory approaches for the treatment of these incapacitating diseases.</p>