This study determines the relationship between postpartum mothers’ dyadic coping and adjustment strategies and their psychological well-being. The study design was descriptive and correlational; it was conducted in the pediatric outpatient clinic of a maternity hospital in Northern Türkiye. A total of 327 1–12 month postpartum mothers participated in the study. Data were collected using a personal information form, the Dyadic Coping Inventory (DCI), the Revised Dyadic Adjustment Scale (RDAS), and the Psychological Well-Being Scale. Mothers’ behavior as an individual and as a couple in dyadic coping, their perception of their partner’s behavior, and weak dyadic harmony between partners was significantly associated with risk factors affecting mothers’ psychological well-being (p < 0.05). A weak relationship was found between the dimensions of mothers’ psychological well-being and their perception of their own behavior in dyadic coping; a positive moderate relationship was found between mothers’ perception of their partner’s behavior in dyadic coping and behaviors exhibited as a couple in dyadic coping, and the former had a weak positive relationship with the dimensions of dyadic harmony and its subdimensions (p < 0.05). Self-perceived coping behavior, perception of the partner’s behavior, and joint coping behavior in dyadic coping, and weak dyadic harmony between partners were significant risk factors affecting mothers’ psychological well-being. Awareness of these factors by health professionals and individuals will increase the effectiveness of postpartum care and help couples adapt to the transition in the postpartum period, improve mother-father-infant interaction and strengthen dyadic harmony.