Child physical punishment is harmful to children and, as such, is being prohibited by a growing number of countries, including Wales. Parents’ own childhood histories may affect their risks of using child physical punishment. We conducted a national cross-sectional survey of Welsh adults and measured relationships between the number of adverse childhood experiences (ACEs) parents (n = 720 with children aged < 18) had suffered during childhood and their use of physical punishment towards children. Overall, 28.2% of parents reported having ever physically punished a child, and 5.8% reported having done so recently (in the last year). Child physical punishment use increased with the number of ACEs parents reported. Parents with 4+ ACEs were almost three times more likely to have ever physically punished a child and eleven times more likely to have done so recently (vs. those with 0 ACEs). The majority (88.1%) of parents that reported recent child physical punishment had a personal history of ACEs, while over half reported recently having been hit themselves by a child. Child physical punishment is strongly associated with parents’ own ACE exposure and can occur within the context of broader conflict. Prohibiting physical punishment can protect children and, with appropriate family support, may help break intergenerational cycles of violence.