The One Health approach recognizes the interdependence of human, animal, and environmental health but has focused on zoonotic diseases and ecological disruption, with comparatively little attention to mental health. This article examines links among environmental change, zoonotic disease dynamics, human–animal relationships, and mental health and proposes a framework for integrating mental health into One Health. A structured search of literature published from 2010 to 2025 was conducted using PubMed, Scopus, and Google Scholar. Evidence indicates that environmental disruption, zoonotic outbreaks, and human–animal interactions affect mental health through overlapping pathways. Climate change and ecological degradation are associated with anxiety, trauma, and livelihood-related distress; zoonotic events may contribute through fear, stigma, social disruption, and economic insecurity; and human–animal relationships may have protective and adverse effects. These findings support a three-pathway model that may strengthen surveillance, preparedness, and policy responses while promoting more preventive and equitable approaches to health.