To report demographics, clinical signs, physical examination, diagnostic test results, surgical findings, and prognostic factors for in-hospital postoperative mortality following biliary peritonitis surgery in dogs. Retrospective, multi-institutional cohort study. Thirty-three client-owned dogs. The medical records of dogs that underwent surgery for biliary peritonitis between 2015 and 2021 were reviewed. Dogs were included if they had a definitive diagnosis of biliary peritonitis and a surgery report. Information on demographics, clinical signs and duration, physical examination findings, laboratory and diagnostic imaging results, surgery, perioperative medical treatment, and complications for each patient was obtained. Statistical analyses were performed to identify risk factors that affected survival. Cholecystectomy was the procedure most frequently performed (31/33, 94%). The overall mortality rate was 36% (12/33). Survival was affected negatively by hyperbilirubinemia (p = .049), administration of vasopressors (p = .002), renal dysfunction (p = .008), and number of postoperative complications (p = .005). A mortality rate of 50% was observed in dogs with a total bilirubin level greater than 60.5 μmol/L. There was no difference in mortality rate between septic and nonseptic biliary effusions. New prognostic factors associated with in-hospital postoperative mortality in dogs treated surgically for biliary peritonitis were identified, while others that had been reported previously were confirmed. A preoperative bilirubin threshold value associated with a 50% mortality was identified. Additional information that could help to predict survival in dogs with biliary peritonitis has been provided. However, further research is warranted.