Accumulating evidence suggests that psychological distress during pregnancy is linked to offspring risk for externalizing outcomes (e.g., reactive/aggressive behaviors, hyperactivity, and impulsivity). Effect sizes across studies have varied widely, however, due to differences in study design and methodology, including control for the confounding continuation of distress in the postnatal period. Clarifying these inconsistencies is necessary to guide the precision of prevention efforts and inform public health policies. A meta-analysis was conducted with 55 longitudinal studies to investigate the association between prenatal psychological distress (anxiety, depression, and perceived stress) and offspring externalizing behaviors. Results revealed a significant but small effect (r = .160) of prenatal distress on externalizing behaviors. The magnitude of the prenatal effect size remained largely unchanged after adjusting for postnatal distress (r = .159), implicating a unique effect of psychological distress during the prenatal period in the etiology of externalizing behaviors. Moderation tests showed that prenatal effects did not vary based on type and timing of psychological distress during pregnancy. Greater instability of distress from prenatal to postnatal periods predicted larger effects. Prenatal effects were comparable across most externalizing outcomes, consistent with the common comorbidity of externalizing spectrum disorders, although effects appeared smaller for nonaggressive rule-breaking (vs. aggressive) behaviors. Significant associations persisted across all developmental periods, appearing slightly larger in early childhood. We discuss these results in the context of developmental and psychobiological theories of externalizing behavior, offer preliminary clinical and public health implications, and highlight directions for future research including the need for longitudinal studies with more racially and socioeconomically diverse families.