Objectives This systematic review thematically synthesised qualitative research exploring men's experiences of their partner's postnatal mental health problems and their impact on men's emotional wellbeing, relationships and support needs. Maternal postnatal mental health problems impact women and their infants. Recognition of the role that men play in supporting women's' recovery and infants' development is growing. However, less is known about how maternal postnatal mental health problems affect men and how they wish to be supported. Methods A systematic review of the literature was conducted in January 2018 by searching five electronic databases (PsycINFO, EMBASE, MEDLINE, PubMed and Web of Science). Qualitative research studies published in English exploring men's experiences of having a partner with postnatal mental health problems were included. Twenty papers met the inclusion criteria and were appraised for methodological quality. Data were thematically synthesised. Results In addition to nineteen subthemes, 5 main themes were identified: (1) Being a father, (2) Being a partner, (3) Experiencing negative emotions, (4) The ways in which men cope and (5) Where support is needed. Conclusions Maternal postnatal mental health problems impacted men's roles of being a father and a partner and gave rise to negative emotions. Men coped with these experiences in a number of ways, which were both helped and hindered by personal, social and professional factors. Participants' coping methods were understood in relation to Coping Theory. Recommendations for perinatal mental health professionals included the need for increased public awareness of postnatal mental health.