Purpose <p>To determine the association of religious service attendance with sleep quality and disorders, and test whether lifestyle and health-related factors mediate this association.</p> Methods <p>This cross-sectional study included 5,520 adults surveyed through a virtual, exploratory, population-based survey (Sonar-Brazil, 2023–2024). Multivariate regression models were used to assess the association among religious service attendance, hypothesized mediators (depression, smoking, alcohol use, drug use, diet quality, body mass index, and screen time) and sleep outcomes. We computed estimates for the total effect, average direct effect, average causal mediation effect, and the percentage of the effect mediated by the mediators using the quasi-Bayesian Monte Carlo method, employing a normal approximation with 5000 simulations.</p> Results <p>Decreasing frequency of religious attendance was associated with poorer sleep quality and higher probabilities of sleep disorders, depression, smoking, drug use, increased alcohol consumption frequency, and longer screen time (<i>p</i> &lt; 0.01). Depression had the greatest influence on sleep outcomes in the multivariate analyses and was identified as the primary mediator in the relationship between religious attendance and sleep quality (24%), followed by smoking (3%) and screen time (7%). Similarly, the effect on sleep disorders was mediated by depression, alcohol consumption, and screen time at 12%, 10%, and 3%, respectively.</p> Conclusion <p>Our findings offer unprecedented insights into the relationship between religious attendance and sleep quality among Brazilian adults and contribute to previous research by showing that religious attendance may protect against sleep disturbance through enhancements in mental health, reduced substance use, and a more active lifestyle, illuminating pathways through which religious involvement may impact sleep outcomes.</p>