Objectives: To synthesize the evidence on the effects of exposure to natural environment on mental health to inform future policymaking, practice, and research. Methods: A systematic search of nine major databases and additional sources were conducted using relevant keywords for the natural environment and mental health till November 2019. We included systematic reviews or meta-analyses reporting any measures of associations between the natural environment and mental health. The data on study characteristics and research findings were extracted using the JBI data extraction tool and synthesized narratively.Results: Twenty reviews were included in this umbrella review reporting both correlational and experimental studies. Among diverse population groups, the exposure to the natural environment was associated with improvements in depressive symptoms, anxiety, mood disorders, stress, cognitive and emotional functions, affect, happiness, and overall mental wellbeing. Conclusions: The findings of this review inform beneficial mental health outcomes associated with exposure to the natural environment. This umbrella review suggests collaborative policymaking, advanced research, and evidence-based practice protecting the natural environment and improving mental health across populations.