Background/Objectives: Declining fertility rates pose a major demographic and public health challenge across Europe, including Croatia. Although health literacy and psychological well-being may influence reproductive decision-making, their relationships with fertility attitudes remain unclear. This study examined associations between health literacy, psychological distress, and fertility attitudes among postpartum women and tested whether anxiety and depression mediate the relationship between health literacy and fertility attitudes. Methods: A cross-sectional study included 1,656 postpartum women from seven coastal counties in Croatia. Participants completed validated measures of health literacy (NVS-HR), anxiety (STAI), depression (BDI-M), and breastfeeding attitudes (IIFAS). Results: Higher health literacy was associated with more positive fertility attitudes (r = 0.18, p < 0.001), while anxiety and depression were negatively associated with fertility attitudes (all p < 0.001). Health literacy was also negatively correlated with anxiety and depression. Logistic regression showed that health literacy (OR = 1.21, 95% CI 1.10–1.34), age (OR = 1.08, 95% CI 1.04–1.12), and positive breastfeeding attitudes (OR = 1.03, 95% CI 1.01–1.05) predicted more positive fertility attitudes, whereas depressive symptoms predicted less positive attitudes (OR = 0.74, 95% CI 0.63–0.88; all p < 0.05). Mediation analyses indicated a significant direct effect of health literacy on fertility attitudes (β = 0.020, p = 0.004), but no significant indirect effects through anxiety or depression. Conclusions: Health literacy was independently associated with positive fertility attitudes and may represent an important target for reproductive health promotion and fertility-related decision-making among postpartum women.