There is strong epidemiological evidence to suggest that paternal postnatal depression (PPD) is associated with adverse offspring developmental outcomes in early childhood. However, few large prospective longitudinal studies have examined whether these adverse outcomes persist into later childhood (7 years of age). Furthermore, the offspring outcomes are heterogenous and effect sizes are small to moderate. Thus, it is important to elucidate putative mechanisms, i.e. mediating factors, that underly associations between PPD and offspring adverse developmental outcomes. Such insights are crucial to highlight those at greater risk and develop targeted interventions to reduce adverse outcomes in offspring of depressed fathers. A substantial body of evidence suggests that an important potential mediator is the quality of parenting. Specifically, evidence suggests that PPD disrupts paternal levels of involvement with the offspring and quality of parenting (e.g., bonding, enjoyment, confidence), which, in turn, is associated with adverse offspring outcomes, including emotional and behavioural problems. However, few population-based studies have examined potential explanatory role of fathers’ involvement and parenting in the association between PPD and offspring development using longitudinal mediation models.