The 2017 American College of Cardiology/American Heart Association high blood pressure (BP) guidelines recommend risk assessment of atherosclerotic cardiovascular disease to inform hypertension treatment in adults with elevated BP or low-risk stage I hypertension. The use of coronary artery calcium (CAC) score to guide hypertension therapy has not been adequately evaluated. Participants free of cardiovascular disease were pooled from Multi-Ethnic Study of Atherosclerosis, Coronary Artery Risk Development in Young Adults, and Jackson Heart Study. The risk for incident cardiovascular events (heart failure, stroke, coronary heart disease), by CAC status (CAC-0 or CAC>0) and BP treatment group was assessed using multivariable-adjusted Cox regression. The 10-year number needed to treat to prevent a single cardiovascular event was also estimated. This study included 6461 participants (median age 53 years; 53.3% women; 32.3% Black participants). Over a median follow-up of 8.5 years, 347 incident cardiovascular events occurred. Compared with those with normal BP, the risk of incident cardiovascular event was higher among those with elevated BP/low-risk stage I hypertension and CAC>0 (hazard ratio, 2.4 [95% CI, 1.7-3.4]) and high-risk stage I/stage II hypertension (BP, 140-160/80-100 mm Hg) with CAC>0 (hazard ratio, 2.9 [95% CI, 2.1-4.0]). A similar pattern was evident across racial subgroups and for individual study outcomes. Among those with CAC-0, the 10-year number needed to treat was 160 for elevated BP/low-risk stage I hypertension and 44 for high-risk stage I or stage II hypertension (BP, 140-160/80-100 mm Hg). Among those with CAC>0, the 10-year number needed to treat was 36 and 22, respectively. Utilization of the CAC score may guide the initiation of hypertension therapy and preventive approaches to personalize cardiovascular risk reduction among individuals where the current guidelines do not recommend treatment.