Using a mixed-methods design, the study provides the first quantitative estimates of leprosy case detection delay, patient delay, and health system delay in southern Nigeria, while also exploring the behavioural and health system factors contributing to delayed diagnosis. We found exceptionally prolonged delays, driven by a combination of geographic barriers, reliance on informal care providers, limited awareness of early symptoms, and gaps in diagnostic capacity. Importantly, our findings suggest that delays commonly attributed to patients are strongly influenced by broader health system accessibility challenges. These findings have direct implications for public health policy, health service delivery, community-based disease surveillance, and neglected tropical disease control in Nigeria and other endemic settings.