The relation of progression of type 2 diabetes and detailed fasting glucose level with risk of atrial fibrillation (AF) is not well known. A total of 6,199,629 subjects not diagnosed with AF who underwent health check-up in 2009 were included from the Korean National Health Insurance Service database. Risk of AF was compared among subjects with normal fasting glucose (NFG), subjects with impaired fasting glucose (IFG), patients with diabetes duration <5 years (early diabetes mellitus DM), and patients with diabetes duration ≥5 years (late DM). Next, risk of AF stratified by fasting glucose level per 10 mg/dL was assessed. During a mean follow-up of 7.2 years, the risk of AF significantly increased across the time course of type 2 diabetes (adjusted hazard ratio (aHR) 1.04, 95% confidence interval (CI) 1.02 to 1.05 for IFG; aHR 1.06, 95% CI 1.04 to 1.08 for early DM; aHR 1.09, 95% CI 1.07 to 1.11 for late DM). The risk of AF was significantly higher in subjects who progressed to type 2 diabetes in the IFG group. Risk of AF increased with a 10 mg/dL increment of fasting blood glucose (p-for-trend <0.0001). However, there was a U-shape relationship between fasting blood glucose and risk of AF in those who received antidiabetic medication. In conclusion, the risk of AF increased with the time course of type 2 diabetes. However, low blood glucose in antidiabetic medication user was associated with an increased risk of AF.