BACKGROUND: Mental disorders represent a major public health challenge, exerting significant pressure on health systems and societies worldwide. Addressing persistent knowledge gaps in their epidemiology and adequate care requires robust population-based data. This article illustrates how a large-scale health claims database can advance research on mental disorders and inform public health decision-making, using the French national health data system (SNDS) as an example. METHODS: We conducted a thematic mapping of studies that used the SNDS to investigate mental disorders from a public health perspective. Relevant studies were identified through the collective expertise of the Mental Disorders Working Group within the ReDSiam network, a national expert group dedicated to developing and validating algorithms for use within the SNDS. Sources included presentations at the group meetings, scientific conferences, and existing literature. RESULTS: First, the SNDS, particularly when combined with prospective cohorts, enables large-scale research on factors associated with the onset of mental disorders, ranging from early-life exposures to adverse life events. Second, it supports the comprehensive epidemiological surveillance of these conditions by facilitating the development of refined detection algorithms and enabling the monitoring of temporal and spatial trends. Third, it allows advanced analyses of care trajectories for individuals with mental disorders, adopting a whole-system approach capturing pathways across services. CONCLUSION: The SNDS offers unprecedented opportunities to advance public health research on mental disorders. Despite limitations, notably regarding clinical and socio-economic information, ongoing methodological advances and broader data integration will further strengthen its contribution to guiding prevention and care strategies in France.