Background Dispositional gratitude has been implicated as a psychological characteristic that may modulate risk for mental health outcomes. Using a population-based sample of U.S. military veterans, this study evaluated the association between dispositional gratitude and the development of psychopathology and suicidal behaviors over a 7-year period. Methods A nationally representative sample of U.S. veterans was surveyed at four timepoints across seven years. Analyses were restricted to veterans without incident outcomes at baseline. Multivariable analyses were conducted to examine the relation between baseline levels of dispositional gratitude and risk of developing (a) major depressive disorder (MDD), generalized anxiety disorder (GAD), or posttraumatic stress disorder (PTSD); (b) suicidal ideation; and (c) suicide attempts. Results A total 9.6% of veterans developed MDD, GAD, and/or PTSD, 9.5% developed suicidal ideation, and 2.8% reported having attempted suicide over the 7-year follow-up period. Among veterans with high levels of dispositional gratitude, incidence was lower for MDD/GAD/PTSD (8.0%), suicidal ideation (6.8%), and suicide attempts (1.5%). Conversely, veterans with low dispositional gratitude were at substantially higher risk of developing MDD/GAD/PTSD (27.7%), suicidal ideation (33.6%), and suicide attempts (20.3%). Conclusions High dispositional gratitude may help protect against the development of psychopathology and suicidal behaviors in U.S. military veterans, whereas low gratitude may increase risk of developing these outcomes. Collectively, these results support the potential utility of enhancing gratitude as part of primary prevention efforts for veterans, service members, and other populations at heightened risk for adverse mental health outcomes.