Nurses are often suboptimally used in HIV care, due to misalignment of training and practice, workflow inefficiencies, and management challenges. We sought to understand nursing workforce capacity and support implementation of process improvement strategies to improve efficiency of HIV service delivery in Tanzania and Zambia. We conducted time and motion observations and task analyses at 16 facilities followed by process improvement workshops. On average, each nurse cared for 45 clients per day in Tanzania and 29 in Zambia. Administrative tasks and documentation occupied large proportions of nurse time. Self-reported competency was low at baseline and higher at follow-up for identifying and managing treatment failure and prescribing antiretroviral therapy. After workshops, facilities changed care processes, provided additional training and mentorship, and changed staffing and supervision. Efficiency outcomes were stable despite staffing increases. Collaborative approaches to use workforce data to engage providers in improvement strategies can support roll-out of nurse-managed HIV treatment.