Aim: The aim of this study was to explore fathers’ mental health during the peripartum period, how stress contributed to psychological distress and loneliness and the ways in which social support moderated these outcomes. Method: This research used a convergent mixed methods design. Both quantitative and qualitative data were collected. In the quantitative strand, The Cohen Perceived Stress Scale, The Edinburgh Postnatal Depression Scale, The DeJong Gierveld Loneliness Scale and The Multidimensional Scale of Perceived Social Support were administered during the third trimester of the prepartum period and again at 3 and 6 months postpartum. Data was collected across 3 waves from February 2021 until October 2021. A total of 91 fathers participated at wave 1, 50 fathers participated at wave 2, and 24 fathers participated at wave 3. In the qualitative strand, one-to-one semi structured interviews were conducted to explore fathers’ experiences with postpartum social support and loneliness. Data was collected from 12 fathers from April 2021 until July 2022. Results: The quantitative strand of this study found 1) social support did not significantly moderate the relationship between perceived stress and psychological distress and 2) social support did not significantly moderate the relationship between perceived stress and loneliness during the third trimester of the prepartum period. However, at three months postpartum, social support did significantly moderate the relationship between perceived stress and loneliness. Upon analysing interview transcripts, three key themes were drawn from the data (i) Being the breadwinner (ii) Seeking postpartum social support and (iii) Feeling lonely when lacking postpartum support. Conclusions: Both strands of this research highlight the potential buffering role of social support on the relationship between postpartum stress and loneliness. It is important to target low partner support, low support from family, friends and from other fathers as potentially modifiable factors for peripartum loneliness interventions.