BACKGROUND Little attention has been paid to how well the American Heart Association's cardiovascular health (CVH) score predicts early‐onset diabetes in young adults. We investigated the association of CVH score with early‐ and later‐onset diabetes and with subsequent complications of diabetes. METHODS AND RESULTS Our sample included 4547 Black and White adults in the CARDIA (Coronary Artery Risk Development in Young Adults) study without diabetes at baseline (1985–1986; aged 18–30 years) with complete data on the CVH score at baseline, including smoking, body mass index, physical activity, diet quality, total cholesterol, blood pressure, and fasting blood glucose. Incident diabetes was determined based on fasting glucose, 2‐hour postload glucose, hemoglobin A1c, or self‐reported medication use throughout 8 visits for 30 years. Multinomial logistic regression was used to assess the association between CVH score and diabetes onset at age <40 years (early onset) versus age ≥40 years (later onset). Secondary analyses assessed the association between CVH score and risk of complications (coronary artery calcium, clinical cardiovascular disease, kidney function markers, diabetic retinopathy, and diabetic neuropathy) among a subsample with diabetes. We identified 116 early‐ and 502 later‐onset incident diabetes cases. Each 1‐point higher CVH score was associated with lower odds of developing early‐onset (odds ratio [OR], 0.64 [95% CI, 0.58–0.71]) and later‐onset diabetes (OR, 0.78 [95% CI, 0.74–0.83]). Lower estimates of diabetic complications were observed per 1‐point higher CVH score: 19% for coronary artery calcification≥100, 18% for cardiovascular disease, and 14% for diabetic neuropathy. CONCLUSIONS Higher CVH score in young adulthood was associated with lower early‐ and later‐onset diabetes as well as diabetic complications.