Objective: Insulin therapy stands as one of the most effective and well-established therapeutic options for managing glycemic control in Diabetes Mellitus (DM). Glargine 300 U/mL (Gla-300) represents a new long-acting insulin analog, which has demonstrated a decrease in the risk of hypoglycemia and a reduction in the total number of injections due to prolonged insulin absorption. In this study, we investigated the long-term effects of Gla-300 on Fasting Plasma Glucose (FPG) and HbA1c levels, as well as the incidence of hypoglycemia in insulin-naive patients admitted to the Internal Medicine outpatient clinic, over a period of 0, 3, 6, 12, and 24 months.. Material and Methods: Between January 2018 and June 2022, insulin-naive patients diagnosed with Type 2 Diabetes Mellitus (T2DM) who initiated treatment with Gla-300 and sought care at the Internal Medicine outpatient clinic were subjected to retrospective analysis. Results: The study included 49 insulin-naive patients. A statistically significant decrease was observed in Fasting Plasma Glucose (FPG) (p = 0.03) and HbA1c (p = 0.02) levels during the 24-month follow-up period of Glargine U-300. Additionally, a significant reduction in both FPG (p < 0.01) and HbA1c (p < 0.01) values was achieved at the time of diagnosis and at 3 months. Hypoglycemia was reported in only 1 patient (2%) during our study, indicating a very low hypoglycemia rate. Conclusion: Diabetes mellitus (DM) poses a significant public health challenge, resulting in economic burden and diminished quality of life. Developed to address these challenges, Gla-300 serves as a long-acting basal insulin that effectively reduces the risk of hypoglycemia while offering targeted glycemic control, as evidenced by our study findings. In Turkey, there is a pressing need for multicenter, prospective real-world studies that incorporate parameters such as insulin dosage and weight monitoring.