BACKGROUND: Infant neurodevelopment in the first years after birth is determined by multiple factors, including parental care and maternal mental wellbeing. In this study, we aim to assess the impact of persistent maternal depressive symptoms during the first 3 months postpartum on infant neurodevelopment at 6 months. METHODS: Using a longitudinal cohort design, 1253 mother-infant pairs were followed up at 7, 45, and 90 days to assess postpartum depressive symptoms using the Edinburgh Postnatal Depression Scale (EPDS); infants were followed up at 6 months to assess neuro-developmental status using the WHO's Infant and Young Child Development (IYCD) tool. A generalized linear regression model was used to assess the association between persistent postpartum depressive symptoms and infant neurodevelopmental delay at 6 months. A generalized linear mixed model (GLMM) with a hospital as a random intercept was used to assess the persistent postpartum depressive symptoms with an IYCD score. Linear regression was used to compare the IYCD scores between exposure groups. RESULTS: In the study population, 7.5% of mothers had persistent depressive symptoms, and 7.5% of infants had neurodevelopmental delay. Infants born to mothers with persistent depressive symptoms had a higher proportion of neurodevelopmental delay than infants born to women without persistent symptoms (48.6% vs 5.1%; p < 0.001). In the adjusted regression model, infants whose mothers had persistent depressive symptoms at 7, 45, and 90 days had a 5.21-fold increased risk of neurodevelopmental delay (aRR, 5.21; 95% CI, 3.17, 8.55). Mean scores in the motor domain (12.7 vs 15.2; p < 0.001) and language domain (6.4 vs 8.5; p < 0.001) were significant when a mother had persistent depression vs. no depression. Mean scores in the general behavioral domain (5.9 vs 10.4, p < 0.001) and the socio-emotional domain (15.4 vs 17.7; p < 0.001) were significantly different when a mother had persistent depression vs no persistent depression. CONCLUSIONS: Our results suggest that 6-month-old infants are at higher risk for neurodevelopment delays if their mother reports persistent symptoms of depression from 7 to 90 days postpartum. The neurodevelopmental delay can be observed in all functional domains. Preventive intervention to reduce maternal postpartum depression may reduce the impact on infant developmental delay.