Purpose: Incidental gallbladder carcinoma (IGBC) is diagnosed in post-cholecystectomy specimens for benign indications, where the role of 2-fluro-2-deoxyglucose positron emission tomography/computed tomography(FDG-PET/CT) is not clearly defined. The present study aimed to assess the benefits of staging and prognosticating with FDG-PET/CT in IGBC. Materials and Methods: A retrospective observational study from a tertiary-care center from January 2010 to July 2020 was performed. The demographic, clinical, histopathological, and treatment-related histories were collected. FDG-PET/CT-image findings were compared with survival outcomes through telephonic follow-up. The chi-square test was used for comparing frequencies. The univariate and multivariate survival estimates were analyzed using the Kaplan–Meier analysis and the Cox-proportional hazard model, respectively. Log-rank test was used to compare the Kaplan–Meier curves. Results: The study included 280 postcholecystectomy participants (mean age: 52 ± 11 years; women: 227) of whom 52.1% had open surgery(146/280). Residual disease in the gallbladder fossa (54.8% vs. 36.6%, p = 0.002) and liver infiltration (32.9% vs. 22.4%, p = 0.05) were seen more frequently in open surgery compared to laparoscopic surgery, while anterior abdominal wall deposits were more common in laparoscopy(35.1% vs. 24%,p = 0.041). FDG-PET/CT changed the management in 10% (n = 28) of patients compared to contrast-enhanced CT. The median survival was 14 months (95%CI-10.3–17.7). A higher stage of the disease on the FDG-PET/CT (loco-regional disease-HR 4.86, p = 0.006; metastatic disease-HR 7.53, p < 0.001) and the presence of liver infiltration (HR-1.92, p = 0.003) were independent predictors of poor survival outcomes. Conclusion FDG-PET/CT detects residual and metastatic disease in patients with IGBC, enabling the institution of appropriate management and acting as a tool for prognostication of survival.