Exposure to maternal mental health problems during pregnancy and the first year of life has been associated with the development of ADHD. One pathway through which maternal mental health may influence children's outcomes is via its effects on parenting. This study aimed to investigate the mediating role of parenting behavior in the pathway between maternal postnatal distress and later symptoms of ADHD in the child. Biological mothers living with their children participating in the Longitudinal Study of Australian Children with data available from waves 1 (child age 3-12 months) and 5 (child age 8-9 years) were included in the current study (n = 3456). Postnatal distress was assessed by parent report at wave 1. Parenting warmth, hostility and consistency were assessed by parent report at wave 5. ADHD status at wave 5 was ascertained by parent report of the child having a diagnosis of ADHD/ADD or by elevated ADHD symptoms by both parent and teacher report. There was evidence of an indirect pathway from maternal postnatal distress to child ADHD at age 8-9 years via parenting hostility, but not through parenting warmth or consistency, even after accounting for concurrent maternal mental health. Our findings highlight the importance of early identification and intervention for maternal postnatal distress, as treatment may prevent mothers from developing hostile parenting practices and also disrupt the pathway to ADHD in their offspring.