Background: The extent of intergenerational transmission of child maltreatment is unclear due to methodological limitations in previous studies. In this study, we aimed to examine factors associated with intergenerational transmission of child maltreatment and quantify its extent in a population sample over a 30-year period in South Australia. Methods: In this retrospective cohort study, we used linked administrative data from the South Australian Birth Registry to identify dyads of mothers and their children both born in South Australia between July 1, 1986, and June 30, 2017. Three child protection system (CPS) outcomes (any CPS involvement, substantiated maltreatment, and time spent in out-of-home care) were computed from data obtained from the South Australian Department for Child Protection. Multivariable Cox regression models were used to estimate hazard ratios (HRs) for child CPS outcomes according to their mother's CPS exposure. Findings: 38 556 unique mother–child dyads were included. 458 (2·0%) of 23 437 children whose mothers had no CPS involvement in childhood had a substantiated report of maltreatment and 127 (0·5%) spent time in out-of-home care. By comparison, 970 (22·1%) of 4382 children whose mothers experienced substantiated maltreatment in childhood had substantiated maltreatment and 469 (10·7%) spent time in out-of-home care. After adjusting for potential confounders, children of mothers with any CPS involvement in childhood had an increased risk of CPS contact compared with children whose mothers had no CPS involvement; this risk was greatest for children of mothers who had both substantiated maltreatment and spent time in out-of-home care (HR 6·25 [95% CI 5·59–6·98] for any CPS involvement, 13·69 [10·08–16·92] for substantiated maltreatment, and 25·78 [18·23–36·45] for any time in out-of-home care). Risks of child CPS outcomes were substantially increased for children of mothers who had a first CPS notification under the age of 1 year or who had any CPS notification at age 13–17 years. Interpretation: Children are at high risk of maltreatment if their mother experienced maltreatment as a child. Assisting survivors of childhood maltreatment, particularly female survivors, provides a crucial intervention opportunity to help prevent further child abuse and neglect. Funding: Australian National Health and Medical Research Council; Channel 7 Children's Research Foundation.