Both parental psychological well-being (e.g., depressive symptoms) and parental relationship functioning (e.g., negative communication) are common parental risk factors for dysfunctional parenting. The spillover process from these parental characteristics to dysfunctional parenting is assumed to be amplified by parental stress, which is particularly common among mothers and fathers of young children. However, few studies have examined dyadic spillover processes from parental risk factors and parental stress on parenting in early childhood. In the current study, we first examined direct actor and partner effects of parents' depressive symptoms and negative communication at 10 months postpartum on dysfunctional parenting at 48 months postpartum in 168 primiparous mixed-gender couples. Second, we analyzed indirect effects via one's own and the partner's parental stress at 36 months postpartum using Actor-Partner Interdependence Mediation Models (APIMeM). We found direct actor effects for mothers' depressive symptoms and negative communication on their dysfunctional parenting. Additionally, indirect actor effects were found for depressive symptoms and negative communication among mothers and fathers. Specifically, mediating effects of depressive symptoms and negative communication on one's dysfunctional parenting through one's parental stress were found. There were no indirect partner effects through parental stress. These findings highlight the important role of parental stress in early childhood as a mediator between both individual and relationship parental risk factors and dysfunctional parenting. These results further underscore the importance of longitudinal dyadic analyses in providing early and tailored interventions for both mothers and fathers of young children.