In sub-Saharan African settings like the Democratic Republic of the Congo, high-quality care during childbirth and the immediate postpartum period is lacking in public facilities, necessitating multipronged interventions to improve care. We used a pre-post design to examine the effectiveness of a low-dose, high-frequency capacity-building and quality improvement (QI) intervention to improve care for women and newborns around the day of birth in 16 health facilities in Kinshasa, Democratic Republic of the Congo. Effectiveness was assessed based on changes in provider skills, key health indicators, and beneficiary satisfaction. To assess changes in the competency of the 188 providers participating in the intervention, we conducted objective structured clinical examinations on care for mothers and newborns on the day of birth, immediate postpartum family planning (PPFP) counseling and method provision, and postabortion care before and after implementation of training and at 6 and 12 months after training. Interrupted time series (ITS) analysis techniques were used to analyze routine health service data for changes in select maternal, newborn, and postpartum outcomes before and after the intervention. To assess changes in clients' perceptions of care, 2 rounds of telephone surveys were administered. Before the intervention, less than 2% of participating providers demonstrated competency in skills. Immediately after training, more than 80% demonstrated competency, and 70% retained competency after 12 months. ITS analyses show the risk of early neonatal death declined significantly by 9% (95% confidence interval [CI]=4%, 13%, P<.001), and likelihood of immediate PPFP uptake increased significantly by 72% (95% CI=53%, 92%, P<.001). Client satisfaction improved by 58% over the life of the project. These findings build on previous studies documenting the effectiveness of clinical capacity-building and QI approaches. If implemented at scale, this approach has the potential to substantively contribute to improving maternal and perinatal health in similar settings.