Background Hypertension, among diabetic patients, is a worldwide public-health challenge and a number one modifiable risk factor for other cardiovascular diseases and death. The prevalence of hypertension among the diabetic population is nearly twice of nondiabetic patients. Screening and prevention of risk factors for hypertension based on evidence from local studies is required to minimize the burden of hypertension among diabetic patients. This study is aimed at assessing the determinants of hypertension among diabetic patients in Wolaita Sodo University Comprehensive Specialized Hospital, Southern Ethiopia, 2022. Methods Facility-based unmatched case-control study design was conducted from March 15 to April 15, 2022, at the outpatient diabetic clinic, Wolaita Sodo University Comprehensive Specialized Hospital. A total of 345 diabetic patients were selected using systematic random sampling techniques. Data were collected using a structured questionnaire by interviewing and extracting from the medical chart of patients. Bivariate logistic regression followed by multiple logistic analysis was used to identify the determinants of hypertension among diabetic patients. A p-value less than 0.05 is considered to be statistically significant. Results The significant determinants of hypertension among diabetes patients were being overweight [AOR = 2.06, 95% CI (1.1, 3.89), P = 0.025], being obese [AOR = 2.64, 95% CI (1.22, 5.70), P = 0.013], lack of Moderate intensity exercise [AOR = 2.41, 95% CI (1.36,4.24), P = 0.002], age [AOR = 1.03, 95% CI (1.01, 1.06), P = 0.011], Type 2 diabetes mellitus [AOR = 5.05, 95% CI (1.28, 19.88), P = 0.021], duration of diabetes mellitus ≥ 6 years [AOR = 7.47, 95% CI (2.02, 27.57), P = 0.003], diabetic nephropathy [AOR = 3.87, 95% CI (1.13, 13.29), P = 0.032], and urban residence [AOR = 2.11, 95% CI (1.04,4.29), P = 0.04]. Conclusion Being overweight and obese, lack of moderate-intensity exercise, age, type 2 diabetes mellitus, duration of Diabetes ≥ 6 years, presence of diabetic nephropathy, and being urban residents were significant determinants of hypertension among diabetic patients. These risk factors can be targeted by health professionals for prevention and earlier detection of hypertension among diabetic patients.