Type 2 Diabetes Mellitus (T2DM) poses a significant and growing public health challenge in Nigeria, largely due to its chronic nature and the high cost of long-term management. In a healthcare system heavily reliant on out-of-pocket payments, many patients face substantial financial hardship, which can compromise treatment adherence and health outcomes. This study examined whether the National Health Insurance Scheme (NHIS) reduces the financial burden of T2DM care among patients in Enugu State, Nigeria. A quantitative cross-sectional comparative design was adopted, involving 400 respondents (200 NHIS-insured and 200 uninsured) selected through a multistage sampling technique. Data were collected using a structured questionnaire covering out-of-pocket expenditure, affordability of care, and coping mechanisms. Descriptive statistics and inferential analyses, including independent samples t-tests and chi-square tests, were conducted at a 0.05 level of significance. Findings revealed that uninsured patients incurred significantly higher mean monthly out-of-pocket expenditure (₦40,367) compared to insured patients (₦22,419) (p < 0.001). Uninsured respondents were more likely to pay fully for medications (85.0%), borrow money (58.0%), skip medication (61.0%), and delay clinic visits (60.0%) due to financial constraints. In contrast, insured patients reported significantly higher affordability of medications and clinic services, lower financial stress, and reduced household economic impact (p < 0.001). The study concludes that NHIS significantly reduces the financial burden of T2DM care and enhances access to essential health services. Expanding and strengthening health insurance coverage is therefore critical for improving financial risk protection and advancing universal health coverage in Nigeria.