Despite growing research on maternal mental health, evidence from low- and middle-income countries, particularly in Africa, remains limited and fragmented. We provide context-specific evidence in the post-COVID era and address an important gap in the literature on socioeconomic vulnerability and maternal mental health. This study investigates the effect of socioeconomic deprivation on postpartum depression and post-traumatic stress disorder among postpartum women using validated assessment tools. Maternal mental health outcomes are assessed using the Edinburgh Postnatal Depression Scale (EPDS) and the Peritraumatic Distress Inventory (PDI), while socioeconomic deprivation is measured using the multidimensional EPICES score. Our study is a multicenter cross-sectional observational study conducted in three hospitals in Casablanca and Rabat, Morocco. A total of 527 women who consent to participate are consecutively recruited at the end of their maternity stay between June 2024 and June 2025. Descriptive analyses show that 26.9% (95% CI: 23.3–30.9%) of women screen positive for postpartum depression and 34.2% (95% CI: 30.2–38.3%) for post-traumatic stress disorder, with 73.2% (95% CI: 69.3–76.9%) classified as socioeconomically deprived. Multivariate logit models reveal that socioeconomic deprivation, measured using both the continuous EPICES score and the dichotomized EPICES indicator, independently increases the risk of postpartum depression (β = 0.028, p < 0.01; β = 0.631, p < 0.05) and post-traumatic stress disorder (β = 0.030, p < 0.01; β = 1.018, p < 0.05). Sensitivity analyses using detailed socioeconomic characteristics confirm the robustness of these effects. The findings underscore the significant impact of socioeconomic disadvantage on maternal mental health and highlight the need for integrated interventions addressing both social and medical determinants of postpartum psychological well-being in developing-country settings.