Background: The objective of this research was to see how Dexmedetomidine affected the onset and duration of brachial plexus block and postoperative analgesia in individuals having upper limb procedures. Methods: This quasi-experimental study was conducted in the Department of Anaesthesia, Rajshahi Medical College Hospital, and Tertiary Hospital in Rajshahi, Bangladesh. From June 2018 to December 2020. There were two groups of (n=60) adult patients randomly assigned to upper-limb and hand procedures each. When it came to the control group, they were given the same amount of Dexmedetomidine (dexmed) as the dexmedetomidine (dexmed) group. Still, they were also given the same amount of 0.75% bupivacaine and 2% lidocaine (with adrenaline) as the dexmedetomidine (dexmed) 1 μg/kg. Ultrasound-guided supraclavicular brachial plexus block administered a total of 0.5 mL/kg in both groups. In addition to hemodynamic stability, patients were monitored for postoperative pain, analgesia duration, and side effects. Results: The dexmed group had a faster onset of motor blockade and a longer duration of sensory and motor blockade (P < 0.0001). For the dexmed group, the postoperative analgesic period was also prolonged compared to that of controls 12 [10.5–13.5] hours and 17 [10.5–19.5] hours in the control and dexmed group, respectively [95% confidence interval, −5 {−5, −4}, P < 0.0001]). Within the first 24 hours following surgery, the dexmed group used rescue analgesics less frequently. (P < 0.0001). Except for 8 and 10 hours after surgery, postoperative pain scores were equivalent between groups when pain levels were lower in the dexmed group. More sedated individuals in the dexmedetomidine group remained sedated for 2 hours longer. (P < 0.0001). We did not have any occurrences of bradycardia, hypotension, respiratory depression, or disorientation. Conclusions: According to our findings, adding Dexmedetomidine to Bupivacaine-lidocaine increased the duration of the supraclavicular brachial plexus block and reduced postoperative analgesia in patients with upper limb surgery.