PURPOSE Despite the growing recognition of the importance of hypertension in patients with cancer, little is known about whether high blood pressure (BP) among patients with cancer is associated with incident heart failure (HF) and other cardiovascular disease (CVD) events and what BP levels are linked to these events. We examined the association of BP classification on the basis of the 2017 American College of Cardiology/American Heart Association BP guideline with the risk of HF and CVD events in patients with cancer. METHODS We studied 33,991 patients with a history of breast, colorectal, or stomach cancer (median age, 53 years; 34.1% men). Patients receiving treatment with BP-lowering medications or having a history of CVD including HF were excluded. Using BP measurements at baseline, 33,991 participants were categorized as having normal BP (n = 17,444), elevated BP (n = 4,733), stage 1 hypertension (n = 7,502), or stage 2 hypertension (n = 4,312). The primary outcome was HF. RESULTS Over a mean follow-up of 2.6 ± 2.2 years, 779 HF events were recorded. After multivariable adjustment, the hazard ratios (HRs) for HF were 1.15 (95% CI, 0.93 to 1.44) for elevated BP, 1.24 (95% CI, 1.03 to 1.49) for stage 1 hypertension, and 1.99 (95% CI, 1.63 to 2.43) for stage 2 hypertension. A stepwise increase in risk with BP categories was also observed in other CVD events. This association was observed even in patients undergoing active cancer treatment. The relationship between hypertension and the risk of developing HF in patients with cancer was confirmed in the Korean National Health Insurance Service database. CONCLUSION Medication-naïve stage 1 and 2 hypertension was associated with a greater risk of HF and other CVD events in patients with cancer. Our results suggest the importance of multidisciplinary collaboration (eg, oncologists and cardiologists) to establish the optimal management strategy for hypertension in patients with cancer.