BACKGROUND: Child maltreatment (CM) is a global public health issue, with reported impacts on health and social outcomes. Evidence on mortality is lacking. In this study, we aimed to estimate the impact of CM on death rates in persons 16 to 33 years. METHODS: A retrospective cohort study of all persons born in South Australia 1986 to 2003 using linked administrative data. CM exposure was based on child protection service (CPS) contact: unexposed, no CPS contact before 16 years, and 7 exposed groups. Deaths were observed until May 31, 2019 and plotted from 16 years. Adjusted hazard ratios (aHRs) by CPS category were estimated using Cox proportional hazards models, adjusting for child and maternal characteristics. Incident rate ratios (IRRs) were derived for major causes of death, with and without CPS contact. RESULTS: The cohort included 331 254 persons, 20% with CPS contact. Persons with a child protection matter notification and nonsubstantiated or substantiated investigation had more than twice the death rate compared with persons with no CPS contact: aHR = 2.09 (95% confidence interval [CI] = 1.62-2.70) to aHR = 2.61 (95% CI = 1.99-3.43). Relative to no CPS contact, persons ever placed in out-of-home care had the highest mortality if first placed in care aged $3 years (aHR = 4.67 [95% CI = 3.52-6.20]); aHR was 1.75(95% CI = 0.98-3.14) if first placed in care aged,3 years. The largest differential cause-specific mortality (any contact versus no CPS contact) was death from poisonings, alcohol, and/or other substances (IRR = 4.82 [95% CI = 3.31-7.01]) and from suicide (IRR = 2.82 [95% CI = 2.15-3.68]). CONCLUSIONS: CM is a major underlying cause of potentially avoidable deaths in early adulthood. Clinical and family-based support for children and families in which CM is occurring must be a priority to protect children from imminent risk of harm and early death as young adults.