Background Postpartum depression and anxiety are significant public health concerns that have serious well documented negative effects on mothers and their families. However, they often remain under-recognized because of limited in-person interactions, time restrictions, lack of adequate support, and pervasive stigmatization. This study investigated the effectiveness of the Smart Mama application on postpartum depression, anxiety levels, and maternal-infant bonding at 12 weeks postpartum. Materials and methods This prospective parallel-group randomized controlled trial included 148 participants from March 1, 2023, to March 31, 2024. Those who agreed to participate were randomly assigned to receive the Smart Mama intervention (n = 74) or routine care (n = 74), using permuted stratified block randomization. The primary outcome was assessed using the Edinburgh Postnatal Depression Scale (EPDS). The secondary outcomes were evaluated using the State-Trait Anxiety Inventory (STAI) and Maternal-Infant Bonding Scale (MIBS) at baseline and the 12-week follow-up using validated standardized tools. Results Compared with the control group, the Smart Mama intervention group showed a significant reduction in postpartum depressive symptoms (P for time × group interaction = 0.04), with a reduction in the EPDS mean score from 9.03 (standard deviation, 2.47) to 5.61 (3.3), whereas the control group showed a change from 9.01 (2.75) to 7.16 (3.1) at 12 weeks post-intervention. Similarly, the Smart Mama intervention led to a significantly greater decrease in both state and trait anxiety levels (both P for time × group interaction < 0.05) compared to the control group. No statistically significant effect on maternal-infant bonding was observed between the intervention and control group (P for time × group interaction = 0.25). Conclusion and implications The Smart Mama intervention significantly reduced postpartum depressive symptoms and anxiety. This study provides empirical evidence and novel insights into the effectiveness of mobile device applications. By integrating a holistic approach, Smart Mama represents a promising and innovative solution for enhancing maternal health outcomes, empowering self-care activities, and overcoming barriers to accessibility. Trial registration The study was registered in the University Hospital Medical Information Network (UMIN) Clinical Trial Registry (ID: (UMIN000050065) on January 19, 2023 (https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000056562).