Suicide has become one of the leading causes of death in the US military in recent years. Understanding the circumstances and factors leading to suicide in military members and identifying appropriate interventions is of high priority for military and civilian leaders. This study prospectively examined and quantified factors associated with risk suicide in a large population of active, Reserve, and National Guard members across all branches of the military during and following service, who were included in the Millennium Cohort Study (N = 151.560). Cohort participants were requested to complete a survey approximately every 3 years regarding mental, behavioural, and functional health, regardless of their current military status. Suicide deaths were identified, during and following military service, using military data from the National Death Index and the Department of Defence Medical Mortality Registry. The finding from this study are not consistent with the assumption that specific deployment-related characteristics, such as length of deployment, number of deployment, or combat experiences, are directly associated with increased suicide risk. Instead, the risk factors associated with suicide in this military population are consistent with other variables, including male sex and mental disorders. Moreover, the US military combat deployments in Iraq and Afghanistan have been associated with a notable upward trend in suicide since 2005. This suggests that knowing the psychiatric history, screening for mental disorders, and early recognition of associated suicidal behaviours combined with high-quality treatment are likely to provide the best potential for mitigating suicide risk.