Abstract Aims Atrial fibrillation (AF) is associated with higher mortality. Biomarkers may improve the understanding of key pathophysiologic processes in AF that lead to death. Using a new multiplex analytic technique, we explored the association between 268 biomarkers and cardiovascular (CV) death in anticoagulated patients with AF. Methods and results A case–cohort design with 1.8- to 1.9-year follow-up. The identification cohort included 517 cases and 4057 randomly selected patients from ARISTOTLE. The validation cohort included 277 cases and 1042 randomly selected controls from RE-LY. Plasma collected at randomization was analysed with conventional immunoassays and the OLINK proximity extension assay panels: CVDII, CVDIII, and Inflammation. Association between biomarkers and CV death was evaluated using Random Survival Forest, Boruta, and adjusted Cox-regression analyses. The biomarkers most strongly and consistently associated with CV death were as follows (hazard ratio for inter-quartile comparison [95% CI]): N-terminal pro-B-type natriuretic peptide [NT-proBNP; 1.63 (1.37–1.93)], cardiac troponin T [cTnT-hs; 1.60 (1.35–1.88)], interleukin-6 [IL-6; 1.29 (1.13–1.47)], growth differentiation factor-15 [GDF-15; 1.30 (1.10–1.53)], fibroblast growth factor 23 [FGF-23; 1.21 (1.10–1.33)], urokinase receptor [uPAR; 1.38 (1.16–1.64)], trefoil factor 3 [TFF3; 1.27 (1.10–1.46)], tumour necrosis factor receptor 1 [TNFR1; 1.21 (1.01–1.45)], TNF-related apoptosis-inducing ligand receptor 2 [TRAILR2; 1.18 (1.04–1.34)], and cathepsin L1 [CTSL1; 1.22 (1.07–1.39)]. Conclusion In this comprehensive screening of 268 biomarkers in anticoagulated patients with AF, the underlying mechanisms most strongly associated with CV death were cardiorenal dysfunction (NT-proBNP, cTnT-hs, CTSL1, TFF3), oxidative stress (GDF-15), inflammation (IL-6, GDF-15), calcium balance, vascular and renal dysfunction (FGF-23), fibrinolysis (suPAR), and apoptosis (TNFR1, TRAILR2). These findings provide novel insights into pathophysiologic aspects associated with CV death in AF. ClinicalTrials.gov identifier NCT00412984 and NCT00262600.