OBJECTIVES: To assess the effectiveness of ultrasound-guided supraclavicular block (UGSCB), performed by emergency physicians, for closed reduction of upper limb fractures or dislocations when compared with Bier block (BB). METHODS: This was an open-label, noninferiority randomised controlled trial. Adults aged ≥ 18 years presenting to an urban district ED with distal radius and/or ulnar fractures requiring emergent reduction were included. Patients were randomised to either UGSCB using 0.75% ropivacaine or BB using 0.5% lignocaine or 0.5% prilocaine, performed by emergency physicians. The primary outcome was patient-reported maximal pain during closed reduction measured via a 10 cm visual analogue scale (VAS), with a noninferiority margin of 2 cm. Secondary outcomes included post-reduction pain at 1-h and adverse events. RESULTS: We enrolled 78 patients with 39 per group. Intention-to-treat analysis showed that maximal pain during closed reduction following UGSCB was noninferior compared with that after BB (UGSCB: median 0.1 cm, interquartile range [IQR] 0 to 2.1; BB: 0.6 cm, IQR 0 to 3.3; difference in medians -0.5 cm, 95% Confidence Interval [95% CI] -1.7 to 0.7 cm; pnoninferiority < 0.001). Pain at 1-h post-intervention was significantly lower in the UGSCB (difference in median -1.8 cm, 95% CI -2.6 to -1.0). There were no between-group differences in adverse events (Odds ratio 2.1; 95% CI 0.18 to 24). CONCLUSIONS: Emergency physician-performed UGSCB provides safe and effective regional anaesthesia that was non-inferior to BB for maximal pain during closed reduction, with the potential advantage of prolonged analgesia.