The prognostic role of high-sensitivity cardiac troponin I (hs-TnI) in patients with newly detected atrial fibrillation (AF) is not well established. We investigate the association of elevated hs-TnI with clinical outcomes and explore the utility of hs-TnI for risk assessment in patients with newly detected AF. From August 2014 to December 2016, 2,361 consecutive patients with newly detected AF were enrolled in a retrospective, single-center registry. Of these, 957 patients were selected and classified into 4 groups according to hs-TnI quartiles. The primary outcome was all-cause death during follow-up. The hs-TnI level was 3.6 ng/L or less in the lowest quartile (Q1), more than 3.6 ng/L to 10.1 ng/L or less in the second quartile (Q2), more than 10.1 ng/L to 22.0 ng/L or less in the third quartile (Q3), and more than 22.0 ng/L in the highest quartile (Q4). The median follow-up period was 19.3 months. In multivariable Cox regression model, Q4 has a higher risk of all-cause death (adjusted hazard ratio [HR]: 3.49; 95% confidence interval [CI]: 1.21 to 10.00; p = 0.02), readmission for heart failure (adjusted HR: 1.75; 95% CI: 1.01-3.05; p = 0.04), and readmission for revascularization (adjusted HR: 3.90; 95% CI: 1.25 to 12.17; p = 0.02) compared with Q1. Independent predictors of all-cause death were renal insufficiency (adjusted HR: 1.96; 95% CI: 1.08 to 3.53; p = 0.02), highest hs-TnI quartile (adjusted HR: 3.30; 95% CI: 1.18 to 9.27; p = 0.02) and anticoagulation therapy (adjusted HR: 0.51; 95% CI: 0.27 to 0.93; p = 0.03). Elevated hs-TnI is independently associated with higher mortality in patients with AF and serves as a valuable prognostic biomarker in patients with newly detected AF.