Background: Reported incidence of acute kidney injury (AKI) is around 5.0–7.5% of all hospitalized patients, and 40% of them are postoperative patients. Major abdominal surgeries account for 3.1–35% of cases of postoperative AKI in various series. The aim of the study was to identify the incidence and risk factors of AKI in peritonitis patients undergoing emergency laparotomy. Materials and methods: Adult patients aged 18–65 years undergoing emergency laparotomy for perforation peritonitis were included in this prospective observational study. Baseline clinical and laboratory data, intraoperative details and postoperative outcome data (AKI at day 7, length of intensive care unit and hospital stay, and mortality) were recorded. Logistic regression model was constructed to predict AKI at day 7. Results: N = 140 patients were included in this study and 69 patients (49.3%) developed AKI within day 7. Larger volume of crystalloid [OR (95% CI) 1.00 (1.00–1.00); p = 0.012], intraoperative vasopressor use (OR 7.42 (2.41–22.83); p < 0.001), intraoperative blood loss [OR 1.004(1.00–1.01); p = 0.003] and the presence of chronic liver disease (CLD) [OR 22.44 (1.68–299.26); p = 0.019] were risk factors for the development of AKI. Acute kidney injury patients had increased mortality at day 90 (24.6% vs 1.4%; p < 0.001), length of ICU stay (3 days vs 0 days, p < 0.001), and length of hospital stay (11 days vs 7 days; p < 0.001). Conclusion: In peritonitis patients undergoing emergency laparotomy, as many as 49% of patients develop AKI within 1 week. The presence of CLD, intraoperative blood loss, and the use of crystalloids and vasopressor increase the odds of developing AKI.