Multiple pathways have been suggested to account for the relationship of adverse childhood experiences (ACEs) and well-being in adulthood, including interpersonal difficulties, the underestimation of one's sense of mastery, and a greater propensity to experience stressors later in life. This study was conducted to examine the association between ACEs and mental health in Canadian Armed Forces (CAF) personnel, and the possible mediating roles of social support, mastery, and combat stressors in that relationship. The study consisted of a prospective analysis involving 3,319 CAF members upon their return from an overseas deployment. Results were that ACEs were associated with poorer mental health (β = -.14, p < .001) and that approximately 42.6% of this relationship could be explained by the mediating effects of low social support, low mastery, and a greater number of combat stressors. The full model, including the covariates, ACEs, social support, mastery, and combat stressors as correlates of postdeployment mental health, was statistically significant with adjusted R(2) = .28, F(9, 3309) = 141.96, p < .001. On the whole, results suggested that social support, mastery, and life stressors may be possible targets for interventions to minimize the impact of ACEs on later mental health in military personnel.