For many years, experts have recognized the importance of studying traumatic brain injury (TBI) among active duty service members and Veterans. A majority of this research has been conducted in Veterans Administration (VA) or Department of Defense (DoD) settings. Though, far less is known about military personnel who seek their medical care outside these settings. Studies that have been conducted in civilian settings have either not enrolled active duty or Veteran participants, or failed to measure military history, precluding study of TBI outcomes by military history. The purpose of the present study was to determine associations between military history and medical (prevalence of 25 comorbid health conditions), cognition [Brief Test of Adult Cognition by Telephone (BTACT)], and psychological health [Patient Health Questionnaire-9 (PHQ-9), Generalized Anxiety Disorder-7 (GAD-7), suicidality (9th item from PHQ-9)] in the first five years after TBI. In this prospective study, we analyzed data from the TBI Model Systems National Database. Participants were 7,797 individuals with TBI admitted to one of 21 civilian inpatient rehabilitation facilities from April 1, 2010, to November 19, 2020, and followed up to five years. We assessed the relationship between military history (any versus none, combat exposure, service era, and service duration) and TBI outcomes. We found specific medical conditions were significantly more prevalent 1-year post-TBI among individuals who had a history of combat deployment (lung disorders, post-traumatic stress disorder (PTSD), and sleep disorder), served in post-draft era (chronic pain, liver disease, arthritis), and served >4 years (high cholesterol, PTSD, sleep disorder). Individuals with military history without combat deployment had modestly more favorable cognition and psychological health in the first five years post-injury relative to those without military history. Our data suggest individuals with TBI with military history are heterogeneous, with some favorable and other deleterious health outcomes, relative to their non-military counterparts, which may be driven by characteristics of service, including combat exposure and era of service.