Diabetes mellitus (DM) is a complex metabolic disorder associated with numerous systemic and oral complications. Oral mucosal lesions (OMLs) represent a less-explored consequence of poor glycemic control in type 2 diabetes mellitus (T2DM). This cross-sectional study investigates the correlation between glycemic control and the prevalence of OMLs in T2DM patients. A total of 250 participants were categorized based on their glycated hemoglobin (HbA1c) levels into well-controlled (HbA1c ≤7%), moderately controlled (HbA1c 7.1–8.9%), and poorly controlled (HbA1c ≥9%) groups. Results revealed a significantly higher prevalence of OMLs in patients with poor glycemic control (p < 0.001). Specific lesions such as candidiasis, lichen planus, and xerostomia were notably more frequent among these patients, correlating strongly with elevated HbA1c levels. Statistical analyses underscored that poor glycemic control is an independent risk factor for the development of OMLs. This study provides new insights into the intricate relationship between metabolic control and oral health in T2DM patients, emphasizing the necessity of integrated healthcare approaches to mitigate these oral complications.