Background The ECG is a simple, noninvasive screening method for cardiovascular disease and arrhythmia. The impact of ECG abnormality on mortality is not certain in low‐risk populations. To address this, we evaluated the association between ECG abnormality and mortality. Methods and Results We retrospectively assessed baseline ECG and all‐cause mortality and cardiovascular mortality in 660 383 patients presenting for medical check‐ups. Baseline ECG abnormalities were classified according to the Minnesota Code. Among the total 660 383 participants, 23 609 (3.6%) had major and 110 038 (16.7%) had minor ECG abnormalities. All‐cause mortality occurred in 7751 patients (1.1%) and cardiovascular mortality in 1180 (0.18%) over a median follow‐up period of 8.8 years. Major ECG abnormalities were associated with all‐cause mortality (hazard ratio [HR], 1.11 [95%, 1.03–1.2]) and cardiovascular mortality (HR, 1.92 [95% CI, 1.63–2.27]) compared with no ECG abnormalities. All‐cause mortality was associated with right atrial enlargement (HR, 2.11 [95% CI, 1.1–4.07]), left atrial enlargement (HR, 1.76 [95% CI, 1.1–2.84]), sinus tachycardia (HR, 1.52 [95% CI, 1.15–2.01]), complete atrioventricular block (HR, 2.1 [95% CI, 1.05–4.2]), atrial fibrillation (HR, 1.52 [95% CI, 1.26–1.84]), and left ventricular hypertrophy (HR, 1.15 [95% CI, 1.02–1.3]). Cardiovascular mortality was associated with left atrial enlargement (HR, 4.52 [95% CI, 2.15–9.5]), atrial fibrillation (HR, 3.22 [95% CI, 2.33–4.46]), left ventricular hypertrophy (HR, 1.72 [95% CI, 1.35–2.19]), major Q‐wave abnormality (HR, 1.6 [95% CI, 1.08–2.39]), and major ST‐T abnormality (HR, 1.76 [95% CI, 1.01–3.04]). Conclusions ECG abnormalities, including left atrial enlargement, left ventricular hypertrophy, atrial fibrillation, and major Q‐wave and ST‐T abnormalities, were associated with cardiovascular mortality in a low‐risk population.