In recent years mothers have been finding themselves overwhelmed by the need to balance work and maternal duties. Father involvement in childcare has been related to a decrease in mother’s burden in childcare. This association is influenced by multiple aspects, such as the way parents share parenting perspectives and views about child rearing, i.e., coparenting. Nevertheless, the mediating role of coparenting on the association between father involvement and maternal stress has been overlooked. This will be addressed by the current study. A total of 254 Portuguese married/cohabiting mothers of preschool children reported on maternal stress, father involvement in caregiving, and coparenting. Data was collected in public and private schools through questionnaires and online through advertisements in social media. Results show that greater father involvement in direct care was associated with greater maternal stress, but this direction changes when mediated by cooperative coparenting. Moreover, results suggest that when mothers perceived less conflict in coparenting, greater father (in)direct care contributed to decreased maternal stress. The current study supports the notion that fathers involvement and parent’s cooperation account to mothers’ wellbeing, which will improve family dynamics.