Introduction Accurate risk stratification is crucial in the management of acute coronary syndrome (ACS) to guide clinical decision-making. The Thrombolysis in Myocardial Infarction (TIMI) and Global registry of Acute Coronary events (GRACE) risk scores are widely recommended for risk stratification. However, comparative evidence supporting their predictive performance within the Malaysian public healthcare setting remains limited. This study aimed to evaluate and compare the ability of GRACE and TIMI risk scores to predict in-hospital outcome and major adverse cardiac events (MACE) among patients with ST-elevation myocardial infarction (STEMI, non-ST- elevation myocardial infarction (NSTEMI) and unstable angina (UA). Methods This study was a retrospective observational study conducted at Shah Alam Hospital in Selangor, Malaysia. All consecutive patients admitted with ACS between 1 January 2024 and 31 December 2024 were included. GRACE and TIMI risk scores were retrospectively calculated using admission data. The primary outcome was in-hospital mortality and the secondary outcome was MACE. Predictive performance was evaluated using logistic regression, receiver operating characteristics (ROC) curve analysis, calibration testing and net reclassification improvement (NRI). Results A total of 873 patients with ACS were included, comprising of 193 STEMI and 680 NSTE-ACS patients. In STEMI patients, GRACE demonstrated superior discrimination for in-hospital mortality prediction (AUC 0.843 vs 0.798), while both scores showed comparable performance for MACE prediction (GRACE AUC 0.837; TIMI AUC 0.847). In multivariable analysis, GRACE remained an independent predictor of mortality (OR 1.021, 95% CI 1.008–1.034, p = 0.001), whereas TIMI was not statistically significant (p = 0.415). In contrast, among NSTE-ACS patients, GRACE consistently outperformed TIMI for prediction of both in-hospital mortality (AUC 0.750 vs 0.617) and MACE (AUC 0.634 vs 0.568). GRACE retained statistical significance in combined regression models for mortality (OR 1.028, 95% CI 1.014–1.042, p < 0.001) and MACE (OR 1.014, 95% CI 1.008–1.020, p < 0.001), while TIMI lost independent predictive significance. Conclusion While both scores are clinically useful, in STEMI, both scores performed relatively comparably, although GRACE demonstrated superior performance for prediction of in-hospital mortality. In NSTE-ACS, GRACE consistently demonstrated better discriminatory ability, retained independent predictive value, and showed more favourable risk classification compared with TIMI. Keywords: Acute coronary syndrome; GRACE risk score; TIMI risk score; in-hospital mortality; major adverse cardiac events