© 2020 Atrial fibrillation (AF) is a common perioperative arrhythmia. However, its occurrence and implications remain poorly defined in the setting of noncardiac procedures. We sought to define the incidence, prevalence, and prognostic implications of AF among patients with atherosclerotic cardiovascular disease (ASCVD) undergoing noncardiac surgery. Using a previously validated approach that employed unique patient-linked variables in the New York State Inpatient Database from January 1, 2012, to December 31, 2014, the frequency of new-onset and pre-existing AF was determined in adults with ASCVD aged ≥18 years undergoing noncardiac surgery. The secondary outcomes were stroke within 1 month and all-cause mortality. Using multivariable logistic regression models, the factors and outcomes associated with new-onset AF after noncardiac surgery were assessed. Nine surgical subgroups of major noncardiac surgery served as exposure. A total of 184,775 patients were identified during the study period. Age ≥65, anemia, history of heart failure, valvular heart disease, and thoracic surgery were predictors of new-onset AF after noncardiac surgery. Among 3,806 patients (2.5%) developed new-onset AF and 31,603 (17.5%) patient had pre-existing AF. After multivariable-adjusted modeling, new-onset AF was associated with increased odds of stroke within 1 month (odds ratio: 1.31, 95% confidence interval: 1.12 to 1.53; p < 0.001)], mortality (odds ratio: 3.74; 95% confidence interval: 3.30 to 4.24; p < 0.001) and longer length of stay in the hospital (10 days; interquartile range: 6 to 16 days; p < 0.001). New-onset AF portends a poor prognosis in patients with ASCVD undergoing noncardiac surgeries. The risk profile of patients that develop new-onset AF differs across patient phenotypes and by surgical procedure.