Background Hypertension and diabetes frequently coexist. However, little is known about the interaction between high blood pressure (BP) and hyperglycemia in the development of cardiovascular disease (CVD). Methods and Results We conducted an observational cohort study that included 3 336 363 patients (median age, 43 years old; men, 57.2%). People taking BP‐ or glucose‐lowering medications or those with prior history of CVD were excluded. We defined stage 1 hypertension as having systolic BP of 130 to 139 mm Hg or diastolic BP of 80 to 89 mm Hg and stage 2 hypertension as having systolic BP of ≥140 mm Hg or diastolic BP of ≥90 mm Hg. We defined prediabetes as having fasting plasma glucose of 100 to 125 mg/dL and diabetes as having fasting plasma glucose of ≥126 mg/dL. Over a mean follow‐up period of 1185 ± 942 days, 5665 myocardial infarction, 52 475 angina pectoris, 25 436 stroke, 54 508 heart failure, and 12 932 atrial fibrillation events occurred. The BP and fasting plasma glucose categories additively increased the risk of myocardial infarction, angina pectoris, stroke, heart failure, and atrial fibrillation. However, the relative risk of stage 1 and stage 2 hypertension developing into CVD was attenuated with deteriorating glycemic status. Similarly, the relative risk of prediabetes and diabetes developing into CVD was attenuated with increasing BP. For example, the relative risk reduction of stage 2 hypertension for heart failure was 53.5% in individuals with normal fasting plasma glucose, 46.4% in those with prediabetes, and 37.2% in those with diabetes. The robustness of our findings was confirmed using a multitude of sensitivity analyses. Conclusions Although hypertension and hyperglycemia additively increase the risk of developing CVD, the relative contribution of hypertension to the development of CVD decreased with deteriorating glycemic status and that of hyperglycemia was attenuated with increasing BP. Our results indicate a potential interaction between hypertension and hyperglycemia in the development of CVD.