Despite increased research on military veterans, little has examined how UK veterans end up in prison. This study addresses this gap through semi-structured interviews with 35 veteran prisoners, investigating their life courses from childhood, military service, civilian life, and into prison. Childhood difficulties—including pre-service contact with the criminal justice system and experiences of childhood neglect and abuse—shaped the participants’ military service experiences and re-entry to civilian society. In-service loss and trauma often led to mental health problems and substance misuse. Most participants regretted leaving the military and struggled to reintegrate into civilian society, citing loss of structure, purpose, and sense of belonging. Unemployment, homelessness, substance misuse, and mental health problems—exacerbated by loneliness and isolation—influenced later criminal offending and eventual imprisonment.