Background: The positive effect of exercise on blood pressure has been reported in studies that investigated mostly patients with hypertension but without diabetes mellitus. However, the effect of exercise in adults with both hypertension and type 2 diabetes mellitus (T2DM) is unclear, and no systematic review and meta-analysis has been conducted to clarify this effect. Objective: This study was a systematic review and meta-analysis designed to investigate the effects of exercise on adults with both hypertension and T2DM. Methods: Studies were selected using electronic databases. Data were extracted using a standardized protocol. The risk of bias was assessed using Cochrane Collaboration's tool. To estimate the effect size, a meta-analysis of the studies was conducted. Results: Of 3207 publications identified, 8 trials were used to estimate the effect size of exercise. Effect sizes (weighted mean difference [WMD]) were heterogeneous, and random-effects models were used. Exercise was effective for systolic blood pressure (WMD, -5.25 mm Hg; 95% confidence interval [CI], -8.39 to -2.12), diastolic blood pressure (WMD, -3.16 mm Hg; 95% CI, -4.91 to -1.40), body mass index (WMD, -1.47 kg/m; 95% CI, -2.39 to -0.55), and waist circumference (WMD, -2.91 cm; 95% CI, -5.68 to -0.15). In subgroup analyses, aerobic exercise seemed to be the most effective intervention for lowering systolic (WMD, -9.43 mm Hg; 95% CI, -13.63 to -5.23) and diastolic (WMD, -5.90 mm Hg; 95% CI, -7.69 to -4.11) blood pressure. Conclusions: Exercise seemed effective in reducing systolic and diastolic blood pressure, with subgroup analyses indicating that this effect was most profound with aerobic exercise.