Background: Magnesium sulfate, N‑methyl‑d‑aspartate receptor antagonist, has both analgesic and sedative properties. Aim: The aim was to evaluate the analgesic efficacy of perioperative intravenous (i.v) magnesium sulfate in severe preeclamptic patients scheduled for cesarean section under spinal anesthesia. Subjects and Methods: A double blind prospective randomized controlled study was designed conducted on 80 patients randomly allocated into two equal groups (n = 40) to receive either bupivacaine heavy intrathecally – Group B (control group) or bupivacaine heavy intrathecally along with i.v magnesium sulfate – Group BM (study group). Magnesium sulfate 40 mg/kg diluted in 100 ml of normal saline was administered over 15 min about 30 min prior to surgery followed by continuous infusion at the rate of 10 mg/kg/h for the next 24 h while the other group received similar volume of normal saline in the same manner. Intraoperatively, patients were monitored for hemodynamic perturbations, respiratory rate, urine output, Apgar score, uterine tonicity, and any other adverse effects. Postoperatively, duration of analgesia, number of rescue analgesics, signs of any magnesium toxicity, and incidence of postpartum eclampsia in the first 24 h were recorded. Data were analyzed using SPSS version 16. Results: At different time intervals, patients in Group BM had less pain than Group B when compared on visual analog scale. Patients in Group BM were significantly more sedated as compared to Group B patients. None of the patients demonstrated bradycardia, hypotensive episodes, hypoxia, or hypoventilation in the postoperative period in the recovery room. There was no significant respiratory depression, Apgar score was comparable, and uterine tonicity was adequate in both the groups. Postoperatively, time required for first analgesic dose was significantly more in Group BM 270 (35.1) min than Group B 223 (31.4) min. There was a significant decrease in total rescue analgesic requirement in Group BM 2.5 (0.4) compared to Group B 3.6 (0.4). Incidence of postpartum eclampsia in study group (one patient) was less than the control group (four patients). Conclusion: Preoperative i.v magnesium sulfate, in severe preeclampsia not only reduces the probability of developing peripartum eclampsia, but also significantly prolongs the duration of analgesia and reduces postoperative analgesic consumption without any significant side effects.