Patients' prognostication around cardiac surgery is key to better assess risk-benefit balance. Preoperative brain natriuretic peptide (BNP) biomarker has been associated with mortality after cardiac surgery, but its added value with EuroScore 2 remains to be confirmed. In a prospective registry cohort of 4,980 patients undergoing cardiac surgery, the prognostic performance of EuroScore 2 and preoperative BNP was assessed regarding postoperative in-hospital mortality. Discrimination feature was evaluated using receiver-operator-characteristics analysis with area under curve (AUROC). Calibration feature was assessed using Hosmer-Lemeshow test. Multivariable analysis was performed to assess the association between covariates and in-hospital mortality. In-hospital mortality was 3.7%. The AUROC of EuroScore 2 was 0.82 (95% confidence interval (95%CI) 0.79-0.85, p < 0.0001). The AUROC of BNP was 0.66 (95%CI 0.62-0.70, p < 0.0001). The combined model with an AUROC of 0.67 (95%CI 0.63-0.71, p = 0.0001) did not yield better AUROC than EuroScore 2 alone (p < 0.0001 in disfavor of the combined model), nor BNP alone (p = 0.79). In multivariable analysis, EuroScore 2 remained independently associated with mortality (adj.OR of 1.12 (1.10-1.14), p < 0.0001), but BNP was not. Preoperative BNP was not an independent risk factor of postoperative mortality and did not add prognostic information, as compared to EuroScore 2 alone.Clinical trial registry Registry for the Improvement of Postoperative OutcomeS in Cardiac and Thoracic surgEry (RIPOSTE) database (NCT03209674).