The current study examined the influence of perceived fairness of household labor and childcare on relationship satisfaction among new parents. Emotional spousal support and negative spousal interactions were analyzed as potential mediators, using cross-sectional and longitudinal data from couples transitioning to parenthood (N = 92). At 9 months postpartum, mothers’ perceived fairness of household labor and childcare were related to their relationship satisfaction through emotional spousal support. Negative interactions mediated the association between mothers’ perceived fairness of childcare and relationship satisfaction, concurrently and longitudinally across the transition. For fathers, there was no evidence of mediation. However, spousal effects of fathers’ perceived fairness of childcare on mothers’ relationship satisfaction was found longitudinally. Overall, the results demonstrate the importance of emotional spousal support and negative spousal interactions when understanding the influence of new mothers’ perceived fairness of family labor on their relationship satisfaction.