Background: There is growing evidence that diabetes mellitus (DM) is an important risk factor for tuberculosis (TB). A significant number of DM patients have poor glycemic control. This study was carried out to find the impact of poor glycemic control on newly diagnosed smear-positive pulmonary tuberculosis patients with type-2 diabetes mellitus in a tertiary care hospital.Methods: In a hospital-based prospective study, newly diagnosed smear-positive pulmonary TB with DM patients were classified as poorly controlled diabetes (HBA1C≥7%) and optimal control diabetics (HbA1c<7%). Patients were started on anti-TB treatment and followed for 2 years for severity and treatment outcome. ANOVA was used for numerical variables in the univariable analysis. Logistic regression analysis was used for multivariable analysis of treatment outcome. The significance level was kept at a P≤0.05.Results: A total of 630 individuals who met the inclusion criteria were analyzed; of which 423 patients had poor glycemic control (PGC) and 207 patients had optimal glycemic control (OGC). The average HbA1c was 10±2.6 and 5±1.50 in the PGC and OGC groups, respectively. The mean symptom score was significantly higher in the PGC group compared with patients in the OGC group (4.55±0.80 vs. 2.70±0.82, P<0.001). PGC was associated with more extensive lung disease, lung cavitation, and positive sputum smear at the baseline. In PGC, sputum smears were significantly more likely to remain positive after 2 months of treatment. PGC patients had significantly higher rates of treatment failure (adj. OR 0.72, 95% CI 0.58-0.74, P<0.001) and relapse (adj. OR 2.83, 95% CI 2.60-2.92, P<0.001)Conclusion: Poor glycemic control is associated with an increased risk of advanced and more severe TB disease in the form of lung cavitations, positive sputum smear, and slower smear conversion. It has a profound negative effect on treatment completion, cure, and relapse rates in patients with pulmonary tuberculosis.