Background: The incidence of diabetes is increasing at an alarming rate throughout the world and poses clinical challenges globally; diabetes is recognized as a syndrome characterized by hyperglycaemias and glucose intolerance, and most patients live in low- and middle-income countries. Poor glycaemic control is a major public health issue among patients with type 2 diabetes mellitus and a significant risk factor for the progression of diabetic complications. Glycaemic control and identifying factors associated with diabetes will help health care providers design programs that improve the quality of services provided to diabetic patients. Objectives: The aim of this study was to assess the magnitude of glycaemic control and its associated factors among type 2 diabetes mellitus patients in Jimma Medical Center. Methods: An institution-based prospective longitudinal study was conducted on 420 type 2 diabetic patients who were admitted to diabetic clinics at the Jimma Medical Center Clinic from May to October 2023. The data were collected through a structured interview questionnaire and a data abstraction format. The data were entered into Epidata version 4.6 and analysed using SPSS version 26 statistical software. Binary logistic regression was used to explore factors associated with poor glycaemic control. Variables with p values < 0.05 were considered to indicate statistical significance. Results: A total of 420 type 2 diabetic patients were interviewed and followed for three months. The median age of the participants was 54 years (IQR = 40–60 years). Among the study participants, 52.38% were females. The median duration of living with diabetes since diagnosis was 10 years (IQR: 5–16 years). Approximately 58.1% of the respondents had uncontrolled fasting blood glucose levels. The factors that were significantly associated with poor glycaemic control were female sex (AOR = 2.576, 95% CI [2.80- 11.479]), older age (≥ 60) (AOR = 2.024, 95% CI [1.794-4.646]), duration of diabetes >10 years (AOR = 3.036, 95% CI [2.616-8.306]), T2DM on insulin +OHA drug regimen (AOR=2.08, 95% CI [298-3.918]), obesity (AOR = 2.18, 95% CI [(1.218-4.218]), and DM complications (AOR = 3.193, 95% CI [2.324- 6.05]), which were found to be independent predictors of poor glycaemic control. Conclusion: The proportion of patients with poor glycaemic control was remarkably high at the JMC. Therefore, more effort should be made to strengthen and disseminate health education programs for diabetes patients on the importance of achieving optimal glycaemic control.