Women in the perinatal period are at increased risk of experiencing self-harm ideation. The current study longitudinally examines the prevalence, trajectories, and correlates of self-harm ideation in a population-based sample of Australian women from pregnancy through to the early years of parenting.Drawing on data from 1507 women participating in a prospective pregnancy cohort study, data were collected during pregnancy, at 3-, 6-, 12-, and 18-months postpartum, and 4-years postpartum. Longitudinal Latent Class Analysis was conducted to identify groups of women based on their responses to thoughts of self-harm at each time-point. Logistic regression analysis was used to identify factors associated with group membership.Approximately 4-5% of women reported experiencing self-harm ideation at each time-point from pregnancy to 4-years postpartum. Cross-sectional analyses revealed that self-harm ideation was most frequently endorsed in the first 12-months postpartum (4.6%), and approximately 15% of women reported self-harm ideation at least once during the study period. Longitudinally, approximately 7% of women had an enduring pattern of self-harm ideation from pregnancy to 4-years postpartum. Women who had experienced a range of preconception and current social health issues and disadvantage were at increased risk of self-harm ideation over time.Limitations included use of brief measures, along with an underrepresentation of participants with particular socio-demographic characteristics.A proportion of women are at increased risk of experiencing self-harm ideation during the perinatal period and in the early years of parenting, underscoring the need for early identification during pregnancy and early postpartum to facilitate timely early intervention.