Abstract: Purpose: The goal of this study was to estimate all-cause mortality among Operations Enduring Freedom, Iraqi Freedom, and New Dawn era service members and veterans and to identify protective and risk factors for mortality. Methods: Using 20 years of longitudinal data from the Millennium Cohort Study (2001–2021), sequential Cox proportional hazard models were conducted to examine demographic, military, and health-related characteristics associated with all-cause mortality among service members and veterans. Results: Among 201,619 participants, 3806 (1.9 %) were deceased by the end of the observation period, with an age- and sex-adjusted incidence of 37.6 deaths per 100,000 person-years. Deployed service members had lower all-cause mortality risk than those who did not deploy. Personnel who experienced combat had higher mortality risk compared with those who did not in unadjusted models; this association was nonsignificant after accounting for health-related factors. Enlisted and Army personnel both had a higher mortality risk, while women and Hispanic individuals had a lower risk. Stressful life events, lower physical health related quality of life, problem drinking, and smoking were also associated with greater mortality risk. Conclusion: These profiles may be useful for developing preventive education and intervention efforts in military and veteran populations to reduce premature mortality.