This longitudinal study examines the timelines of occurrences of intimate partner violence (IPV) on child–mother attachment, as well as the mediating role of maternal postpartum depression (PPD). Using a sample in the United States (N = 2,268), findings suggest that, compared to mothers’ prenatal IPV victimization, postnatal IPV more negatively influences child–mother attachment when the children were at 3 years old, and this negative impact on attachment was partially mediated through maternal PPD. As IPV screening for pregnant women in healthcare settings becomes a common practice, effective IPV and PPD screening postnatally should be broadly implemented to promote maternal mental health and child–mother attachment.