Childhood maltreatment can disturb brain development and subsequently lead to adverse socioemotional and mental health problems across the life span. The long-term association between childhood maltreatment and resting–wake brain activity during adulthood is unknown and was examined in the current study. Forty-one medically stable and medication-free military veterans (M = 29.31 ± 6.01 years, 78% male) completed a battery of clinical assessments and had [18F]-fluorodeoxyglucose positron emission tomography neuroimaging scans during quiet wakefulness. After statistically adjusting for later-life trauma and mental health problems, childhood maltreatment was negatively associated with brain activity within a priori defined regions that included the left orbital frontal cortex and left hippocampus. Childhood maltreatment was significantly associated with increased and decreased brain activity within six additional whole-brain clusters that included the frontal, parietal–temporal, cerebellar, limbic, and midbrain regions. Childhood maltreatment is associated with altered neural activity in adulthood within regions that are involved in executive functioning and cognitive control, socioemotional processes, autonomic functions, and sleep/wake regulation. This study provides support for taking a life span developmental approach to understanding the effects of early-life maltreatment on later-life neurobiology, socioemotional functioning, and mental health.