Abstract: Physical activity may be an important factor for understanding health and psychosocial outcomes following military service. The purpose of this analysis was to evaluate the association between physical activity and biopsychosocial outcomes in post-9/11 Veterans. We also evaluated the interaction of physical activity with posttraumatic stress disorder (PTSD) diagnosis and traumatic brain injury (TBI) history. Data were cross-sectional from 549 post-9/11 Veterans. Hierarchical linear regression models were used to investigate relationships between self-reported physical activity and biopsychosocial outcomes. Physical activity was significantly associated with better outcomes beyond PTSD and TBI, including depression (B = −1.03), neurobehavioral symptoms (B = −1.06), sleep quality (B = −0.36), pain interference (B = −0.18), and quality of life (B = 1.38). Promoting physical activity could enhance mental and physical health in Veterans, independent of PTSD diagnosis or TBI history. Exercise programs may be particularly beneficial for addressing specific biopsychosocial concerns among Veterans.