Abstract: Military reservists occupy a distinct social position, navigating dual roles as civilians and service members, an intersection that requires tailored intervention strategies. Despite their growing role in the total force, the social determinants of health (SDOH) affecting reservists remain underexamined. We were interested in how SDOH (i.e., education, employment status, financial strain, housing, or social support) influences suicidality, depressive symptoms, and wellbeing. As such, this study analyzed data from 4,007 U.S. military reservists, identifying largely positive mental health outcomes, with low levels of suicidality, low depressive symptoms, and moderate to high psychological wellbeing. Financial strain emerged as the most consistent and robust predictor of poor mental health across all outcomes. Regression analyses also highlighted recent homelessness and having legal challenges as key predictors. The findings highlight potential intervention opportunities, particularly for mid-career reservists aged 25-34, who are at a heightened risk of vulnerability. Targeted, multidisciplinary support, including housing stability, financial education, and legal assistance, may improve mental health and individual readiness among military reservists. Future research should examine variation across reserve components and service branches to better tailor services and support utilization.