Growing attention has been placed on examining the family environment as antecedent of attachment, including the coparenting relationship. Parents’ satisfaction with the coparenting relationship may be particularly of interest when parents are at heightened risk for depression, as depression has been consistently linked to negative coparenting, poor quality of parenting, and insecure infant attachment. However, no study has examined the effects of parents’ satisfaction with the coparenting relationship on attachment. The present study examined mothers’ satisfaction with division of childrearing responsibilities, a component of coparenting, and its longitudinal and cross-sectional links with infant disorganized attachment, examining the quality of mothering as a mediator, in a sample of infants and mothers at elevated risk for depression (N = 234). We assessed maternal depressive symptoms at 3, 6, and 12 months of infant age, mothers’ satisfaction with the division of parental responsibilities at 3 and 12 months, the quality of mothering at 6 and 12 months, and infant disorganized attachment at 12 months. Mediation analyses revealed that at 12 months, mothers who were unsatisfied with fathers’ childrearing responsibilities had poorer quality of mothering, which in turn was linked to disorganized attachment in their infants. However, the longitudinal indirect association between satisfaction with childrearing responsibilities at 3 months and disorganization at 12 months mediated by maternal parenting at 6 months was not significant. Findings emphasize the importance of partner support in childrearing for mothers at risk for depression in shaping a healthy relationship between mothers and their infants, particularly as infants get older.