Objective: The triglyceride-glucose (TyG) index, the product of fasting triglycerides and glucose, is a useful and cost-effective marker of insulin resistance (IR). Furthermore, the TyG index is a known IR screening tool in healthy young adults but not in those with atherosclerotic cardiovascular disease (CVD). Thus, this study aimed to evaluate the TyG index as a predictor of CVD in healthy young adults. Methods: This study enrolled 6,675,424 adults aged 20–39 years without CVD from the National Health Information Database. We categorized them by TyG index quartile from 2009–2017. The study outcomes were stroke, myocardial infarction (MI), and mortality. All outcomes were analyzed by Cox proportional hazards regression analysis while controlling for baseline covariates. Results: During a mean 7.4 years of follow-up, 8,506 cases of stroke, 12,312 cases of MI, and 22,667 deaths were recorded. Multivariable-adjusted hazard ratios (HRs) for participants in the highest TyG index quartile demonstrated that they were at higher risk for stroke (HR, 1.253; 95% confidence interval [CI], 1.167–1.346), MI (HR, 1.258; 95% CI, 1.187–1.334), and mortality (HR, 1.151; 95% CI, 1.104–1.200) than those in the lowest TyG index quartile independent of age, sex, smoking, alcohol consumption, physical activity, income, body mass index, blood pressure, and total cholesterol. The HRs for outcomes in the highest quartiles were higher when the TyG index was applied than when triglyceride or fasting glucose alone was applied. Conclusion TyG index, a simple measure reflecting IR, can predict CVD and mortality in young and healthy populations.