Although the negative impact of postpartum depression on parenting behaviors has been well established—albeit separately— for mothers and fathers, the respective and joint impact of both parents' mood on family-group interactive behaviors, such as coparenting support and conflict behaviors between the parents, have not yet been investigated. The aim of this study was to examine the association between parental depressive symptoms and coparenting behaviors in a low-risk sample of families with infants, exploring reciprocity between the variables, as well as gender differences between mothers and fathers regarding these links. At 3 (T1), 9 (T2), and 18 months postpartum (T3), we assessed both parents' depressive symptoms with a self-report questionnaire and observed coparenting support and conflict in triadic mother–father–child interactions. The results revealed that higher maternal depressive symptoms at T1 were associated with lower support at T1 and T2. Conflict at T3 was associated with higher maternal depressive symptoms at T3 and, more surprisingly, with less depressive symptoms in mothers at T2 and fathers at T3. Cross-lagged associations suggested that parental depressive symptoms were more likely to influence coparenting than the reverse. Moreover, maternal depressive symptoms were more likely to be linked to coparenting behaviors than were paternal depressive symptoms. These results confirm that parental—mostly maternal—depressive symptoms, even of mild intensity, may jeopardize the development of healthy family-level relations, which previous research has shown to be crucial for child development.