Type 2 Diabetes Mellitus (T2DM) constitutes a substantial and escalating public health burden across India, with South Indian states exhibiting some of the highest age-standardised prevalence rates in the nation, driven by a convergence of rapid dietary transition, declining physical activity, genetic susceptibility, and urbanisation. This study investigates the determinants of glycaemic control among T2DM patients attending outpatient diabetic clinics in Tamil Nadu and Karnataka, examining the role of structured diabetes education programmes in modifying self-care behaviours and improving HbA1c outcomes over a six-month intervention period.The study enrolled 4,218 participants across twelve clinical sites stratified by urban, peri-urban, and rural location. Baseline HbA1c, fasting plasma glucose, BMI, blood pressure, and lipid profiles were recorded, along with validated self-care scores across dietary adherence, physical activity, medication compliance, blood glucose monitoring, and foot care domains. Participants in the intervention arm received a structured twelve-session Diabetes Self-Management Education (DSME) programme delivered by trained diabetes nurse educators and dieticians, with motivational interviewing components incorporated after session four.At six-month follow-up, intervention arm participants showed a mean HbA1c reduction of 1.9 percentage points compared to 0.4 in the control arm (p<0.001). Self-care scores improved significantly across all five domains in the intervention group. Multivariable logistic regression identified rural residence, sedentary lifestyle, family history, and overweight as independent risk factors for poor glycaemic control, while DSME completion emerged as the strongest protective predictor (adjusted OR 0.52, 95% CI 0.39-0.69). The study provides evidence for scaling structured patient education in primary and secondary care settings across South India as a cost-effective strategy for improving population-level glycaemic outcomes.