Background: Effective regional anesthesia techniques are crucial for optimal pain management in upper limb surgeries. This study compares dexmedetomidine and dexamethasone as adjuvants to bupivacaine in ultrasound-guided supraclavicular brachial plexus block. Methods: This cross-sectional observational study was conducted in the Department of Anaesthesia, Analgesia, and Intensive Care Medicine at Bangabandhu Sheikh Mujib Medical University, Dhaka, Bangladesh, over one year (June 2022 to May 2023). Sixty adult patients undergoing elective upper limb surgeries were randomized into two groups: Group A (dexmedetomidine 1 µg/kg with bupivacaine) and Group B (dexamethasone 4 mg with bupivacaine). Outcomes measured included onset and duration of sensory and motor blocks, duration of analgesia, and adverse events. Results: Group A demonstrated a significantly prolonged duration of analgesia (median: 1027.5 minutes; interquartile range [IQR]: 71.25) compared to Group B (median: 900 minutes; IQR: 108.75; p < 0.001). Sensory and motor block durations were also significantly longer in Group A (p < 0.05). The onset times for sensory and motor blocks were slightly delayed in Group A compared to Group B. No adverse events such as hypotension, bradycardia, or sedation were observed in either group. Conclusion: Dexmedetomidine provides superior prolongation of sensory and motor blocks and postoperative analgesia compared to dexamethasone when used as an adjuvant to bupivacaine in supraclavicular brachial plexus block. Both adjuvants were safe, with no reported complications.