To date, research on social support as a factor affecting the relationship between infant sleep and postnatal depression (PND) has not been widely examined. This study aimed to determine the extent to which social support affects this relationship. The sample consisted of 108 caregivers of children between 6-18 months of age. Participants completed an online survey comprised of the Edinburgh Postnatal Depression Scale, The Social Provisions Scale and The Brief Infant Sleep Questionnaire. Results indicated that parents of children who were sleep disturbed had higher levels of PND and less social support. Correlations between PND and nocturnal sleep (r = -0.231, p =0.016) and nocturnal wakefulness (r = -0.228, p = 0.018) were significant. Social support was also significantly correlated with nocturnal sleep (r = 0.329, p = 0.001) and nocturnal wakefulness (r = 0.199, p = 0.039). A significant negative relationship between social support and PND was found (r = -0.539, p < 0.001). No moderating effect of social support on the relationship between child sleep disturbance and PND was found for either nocturnal sleep duration (b = -0.014, 95% CI [-0.099, 0.071], t = -0.33, p = 0.745) or nocturnal wakefulness (b = 0.065, 95% CI [-0.267, 0.396], t = 0.39, p = 0.700). Overall, the results suggest that social support may have an impact on parental PND and child sleep disturbance. Although a significant moderating effect of social support was not found, the significant correlations support the need for further research in this area.