There are many factors associated with the premature cessation of exclusive breastfeeding. They include demographic, biological, psychosocial, and social factors. Some of these factors are not modifiable, such as age, social status, and education level, as they are not amenable to an intervention. One possible modifiable factor, which may assist women in overcoming breastfeeding difficulties, is fathers' support with breastfeeding. Fathers' favourable attitude and support of breastfeeding positively impacts breastfeeding initiation, duration, and exclusivity. Research on ways to assist fathers in providing support for breastfeeding is needed. The ways in which fathers can provide effective support can best be determined through intervention studies designed to increase fathers' supportive behaviour towards breastfeeding. Specifically, a coparenting framework to guide such interventions would be optimal as coparenting teaches parents to work in partnership towards positive child health outcomes. The purpose of this proposed randomized controlled trial is to evaluate the effects of a coparenting breastfeeding support intervention, delivered to primiparous breastfeeding mothers and the infants' fathers (the breastfeeding woman's male partner, who is jointly responsible for the child). It is hypothesized that this intervention will increase exclusive breastfeeding at 12 weeks postpartum. The secondary outcomes will be breastfeeding duration, perceived breastfeeding support, and coparenting at 6 and 12 weeks. Paternal breastfeeding self-efficacy and infant feeding attitude will be assessed at 6 weeks postpartum.