Background: Postpartum depression (PPD) affects up to 20% of mothers and birthing parents, yet only 1 in 10 receive evidence-based treatment. Left untreated, PPD increases the risk of future depressive episodes, familial disharmony, and offspring problems. This study sought to determine if an online 9-week group cognitive-behavioural therapy (CBT) intervention delivered by mothers who have recovered from postpartum depression (i.e., peers) can effectively improve PPD, anxiety, social support, the mother-infant relationship, and infant temperament in those with PPD. Methodology: During the COVID-19 pandemic, 183 participants were randomized into experimental (received intervention at baseline plus treatment as usual (TAU)) and waitlist control (TAU plus the intervention after a 9-week wait) groups. Participants were ≥18 years of age, had an infant