Since its launch in 2005, the U.S. President's Malaria Initiative's (PMI) investment in malaria case management has evolved based on lessons learned from its support to countries. An initial focus on updating malaria treatment policies to adopt artemisinin-based combination therapies achieved limited success, in part because of the poor quality of diagnostic and treatment services in targeted countries. In response, the PMI supported the development, refinement, and expansion of Outreach Training and Supportive Supervision (OTSS), a quality improvement approach that combines structured, competency-based supervision with corrective measures, including on-the-job training, coaching, troubleshooting, action planning, and timely follow-up. With 15 years of experience, the OTSS approach has been adopted by more than a dozen countries, and its effectiveness in improving the quality of malaria case management services has been documented. Through the PMI Impact Malaria Project, launched in 2018, the OTSS approach was expanded beyond case management of uncomplicated malaria to support quality improvement of inpatient management of severe malaria and malaria in pregnancy services delivered through antenatal care clinics. The OTSS platform also enabled targeted countries to respond rapidly to the COVID-19 pandemic by adding modules related to clinical management and laboratory diagnosis of suspected cases. The OTSS approach has been established as an effective approach to improve the quality of clinical malaria services and can be expanded to cover other health priorities. Further innovations to improve the quality of inpatient and community-based services, and further integration and institutionalization of OTSS into country health systems are needed.