Background: Opioids have been used with peripheral nerve blocks for its synergistic effect to enhance the postoperative analgesic effectiveness of regional block. Nalbuphine, a newer opioid with an analgesic equivalence of morphine, has a ceiling effect on respiratory depression. The aim of the present study was to evaluate the effect of nalbuphine when used as an adjuvant to levobupivacaine on 24-hour postoperative analgesic requirement after brachial plexus block (BPB). Materials and methods: Sixty adult patients of either sex of American Society of Anesthesiologists (ASA) physical status I and II were randomized into two groups of 30 each to receive a total volume of 30 mL of study drug for supraclavicular brachial plexus block (SBPB): Group N—29 mL of 0.5% levobupivacaine with 1 mL of 10 mg nalbuphine; Group S—29 mL of 0.5% levobupivacaine with 1 mL of normal saline. Patients observed for 24-hour postoperative mean requirement of rescue analgesia, that is, diclofenac sodium, block characteristics, visual analog scale (VAS) scores, and the associated complications. Results: Demographic profile was comparable between the two groups. The mean dose of rescue analgesic required between the groups N and S was 127.5 ± 34.96 mg and 150 ± 37.5 mg (p = 0.000), respectively. The average VAS score at different time intervals was highly significant between the two groups (p <0.05). Similarly, block characteristics were statistically significant between the two groups; that is, onset was early, but the duration was prolonged in group N (p <0.05). Complications, although more in group N, were minor and statistically insignificant (p >0.05). Conclusion: Nalbuphine 10 mg as an adjunct to 0.5% levobupivacaine significantly reduced the requirement of rescue analgesia compared to placebo, with no significant major adverse effects.