We aimed to investigate long-term cardiovascular sequelae after coronary artery bypass grafting (CABG) in patients with subclinical hypothyroidism (SCH). All-cause and cardiovascular-related mortality, and cardiovascular events were retrospectively reviewed in 222 euthyroid and 36 SCH patients who underwent CABG. During a mean follow-up period of 8.2 ± 4.1 years, there were 90 incidents of all-cause deaths, 20 cardiovascular-related deaths, 70 major cardiovascular adverse events, 6 myocardial infarctions, 12 unstable anginas, 31 strokes, 23 hospitalizations due to heart failure, 15 atrial fibrillation (AF) events, and 27 coronary revascularizations. The incidence rate of coronary revascularization was significantly higher in patients with SCH (n = 6, 16.6%) than in euthyroid patients (n = 20, 9.0%), with a hazard ratio (HR) of 3.179 (95% confidence interval [CI] 1.174, 8.605; p = 0.023) after adjustment. In subgroup analysis, SCH patients who experienced postoperative AF within 3 months after CABG surgery had a significantly higher risk of coronary revascularization (n = 4, 25.0%) than euthyroid patients without AF (n = 14, 8.9%) after adjustment (HR 11.759, 95% CI 2.747, 50.343, p = 0.001). The frequency of fatal or nonfatal unstable angina was also higher in patients with SCH (n = 2, 12.5%) than in euthyroid patients (n = 4, 2.5%) (HR 16.999, 95% CI 2.242, 128.860, p = 0.006). In conclusion, preoperative SCH is associated with less favorable cardiovascular outcomes, especially coronary revascularization after CABG. Moreover, SCH patients who develop postoperative AF exhibit significantly increased risks of unstable angina and coronary revascularization. Preoperative evaluation of thyroid function may be helpful for predicting long-term outcomes after CABG.