Although the fibrinogen-to-albumin-to-globulin ratio (FAGR) has been proven to be related to coronary artery disease (CAD), the association between the FAGR and acute ST-segment elevation myocardial infarction (STEMI) has not been adequately investigated. This study aimed to evaluate the prognostic potential of the FAGR for STEMI. A total of 1042 patients with STEMI after emergency PCI admitted to the First Affiliated Hospital of Kunming Medical University from June 2018 to January 2023 were enrolled in the study. Patients were divided into a low FAGR group and a high FAGR group according to the median FAGR (2.44). We used Kaplan-Meier plots, restricted cubic spline regression, Cox survival analyses and time-dependent ROC analyses to explore the predictive value of the FAGR for all-cause and cardiovascular mortality. Kaplan‒Meier analysis revealed that the cumulative incidence rates of all-cause and cardiovascular mortality in patients with STEMI were greater in the high FAGR group. Multivariate Cox proportional hazard analysis revealed that the FAGR was an independent predictor of both all-cause and cardiovascular death. In terms of the prediction of all-cause mortality, the FAGR had an area under the ROC curve of 0.720, which was better than that for fibrinogen (AUC = 0.687). In terms of the prediction of cardiovascular mortality, the area under the ROC curve for the FAGR was 0.726, which was also better than that for Fib (AUC = 0.698). The present results suggest that the FAGR may serve as a potential prognostic indicator in patients with STEMI after emergency PCI.