National Policy Index (NPI) for worker mental health and its relationship with enterprise psychosocial safety climate

•Mental ill health is an international public health crisis and current approaches have been ineffective.•We investigate the role of national policy in improving mental health, providing strong evidence that certain national policy objectives do improve mental health via work conditions.•We (1) undertake a global analysis of national occupational health and safety policy for worker mental health and, (2) validate a tool that quantifies national policy approaches in the interests of bolstering mental health through decent work.•Data were collected across 45 diverse countries, such as Colombia, India, Indonesia, China, and Norway. Data were obtained from national experts such as commissioners and federal ministry leaders.•The tool—the National Policy Index (for worker mental health)—correlated with enterprise-level PSC, highlighting the critical role of national policy in protecting worker mental health. Above and beyond national policy, national union density related to enterprise PSC, demonstrating that social action is imperative.