Perinatal depression and anxiety are associated with significant adverse effects for the mother and child. Online cognitive behavioural therapy (iCBT) can provide scalable access to psychological interventions to improve perinatal depression and anxiety, however, few studies have examined the effectiveness of these interventions in routine care. This study investigated the uptake and treatment outcomes of women living in the Australian community who enrolled in a pregnancy or postnatal iCBT program for their symptoms of depression and anxiety. 1502 women commenced iCBT (529 pregnancy and 973 postnatal) and completed measures of anxiety and depression symptom severity, and psychological distress pre- and post-treatment. 35.0 % of women in the pregnancy program and 41.6 % in the postnatal program completed all 3 lessons, with lower pre-treatment depression symptom severity significantly associated with increased likelihood of perinatal program completion. Both iCBT programs were associated with medium pre- to post-treatment effect size reductions in generalised anxiety symptom severity (gs = 0.63 and 0.71), depression symptom severity (gs = 0.58 and 0.64), and psychological distress (gs = 0.52 and 0.60). Lack of control group and long-term follow-up, as well as detailed information on nature of the sample (e.g., health status, relationship status). Additionally, the sample was limited to Australian residents. iCBT for perinatal anxiety and depression was associated with significant symptom improvement. Current findings support the use of iCBT in perinatal populations and its integration within routine healthcare provision.