The present study aimed to investigate interactions between perceptions of quality of intimate partner relationship and postnatal depressive symptoms in members of heterosexual couples 6 months after the birth of their first infant, while controlling for other relevant risk and protective factors. Secondary analysis was conducted on data from a prospective community cohort study of Australian, primiparous women and their partners. The outcome measure was Edinburgh Postnatal Depression Scale score. Quality of intimate partner relationship, personality factors and infant behaviour were assessed using the standardised Intimate Bonds Measure, Vulnerable Personality Style Questionnaire and Barr Chart respectively. Complete data were available for 161 couples. Associations between Edinburgh Postnatal Depression Scale scores and own and partner ratings of the intimate partner relationship were estimated simultaneously using multilevel modelling. When other relevant factors were controlled, relationships in which partners were perceived as critical, coercive or intimidating were associated with significantly more depressive symptoms in individuals (P=0.004) as well as their partners (P=0.008). In both women and men, vulnerable personality traits, coincidental adverse life events and more infant crying and fussing were also associated with significantly more depressive symptoms. Thus, the quality of the intimate partner relationship is significantly associated with postnatal mental health in both women and men, especially in the context of coincidental stressful events including infant crying.