OBJECTIVE: To determine the effectiveness of risk stratification using the Global Registry of Acute Coronary Events (GRACE) risk score (GRS) for patients presenting to hospital with suspected non-ST elevation acute coronary syndrome. DESIGN: Parallel group cluster randomised controlled trial. SETTING: Patients presenting with suspected non-ST elevation acute coronary syndrome to 42 hospitals in England between 9 March 2017 and 30 December 2019. PARTICIPANTS: Patients aged ≥18 years with a minimum follow-up of 12 months. INTERVENTION: Hospitals were randomised (1:1) to patient management by standard care or according to the GRS and associated guidelines. MAIN OUTCOME MEASURES: Primary outcome measures were use of guideline recommended management and time to the composite of cardiovascular death, non-fatal myocardial infarction, new onset heart failure hospital admission, and readmission for cardiovascular event. Secondary measures included the duration of hospital stay, EQ-5D-5L (five domain, five level version of the EuroQoL index), and the composite endpoint components. RESULTS: 3050 participants (1440 GRS, 1610 standard care) were recruited in 38 UK clusters (20 GRS, 18 standard care). The mean age was 65.7 years (standard deviation 12), 69% were male, and the mean baseline GRACE scores were 119.5 (standard deviation 31.4) and 125.7 (34.4) for GRS and standard care, respectively. The uptake of guideline recommended processes was 77.3% for GRS and 75.3% for standard care (odds ratio 1.16, 95% confidence interval 0.70 to 1.92, P=0.56). The time to the first composite cardiac event was not significantly improved by the GRS (hazard ratio 0.89, 95% confidence interval 0.68 to 1.16, P=0.37). Baseline adjusted EQ-5D-5L utility at 12 months (difference -0.01, 95% confidence interval -0.06 to 0.04) and the duration of hospital admission within 12 months (mean 11.2 days, standard deviation 18 days v 11.8 days, 19 days) were similar for GRS and standard care. CONCLUSIONS: In adults presenting to hospital with suspected non-ST elevation acute coronary syndrome, the GRS did not improve adherence to guideline recommended management or reduce cardiovascular events at 12 months. TRIAL REGISTRATION: ISRCTN 29731761.