Background: Advanced biliary tract cancers (BTC) are lethal cancers with limited treatment options and short survival. Median progression-free survival (mPFS) in the ABC-02 trial was 8.0 months with gemcitabine-cisplatin (GC) and 5.0 m with gemcitabine alone in the front-line setting. The ABC-06 trial showed mPFS of 4.0 m with second-line FOLFOX. TP53 mutation is known to be associated with poor prognosis in other cancers, but its impact on survival in advanced or metastatic BTC has not been detailed. Methods: Mutational profiles were obtained from a retrospective database collected via an institutional DNA/RNA sequencing panel, FoundationOne, or Guardant360. Out of 149 patients with TP53 mutations in BTC, 90 had advanced or metastatic BTC treated at a single institution between 2015 and 2021. These patients were not candidates for surgery, radiation, or liver-directed therapy. Results: Intrahepatic, hilar, distal, and gallbladder cancer diagnoses were confirmed in 66, 11, 10, and 3 patients. Median age was 63, with a male:female ratio of 1:1. Poorly, moderately, and well-differentiated adenocarcinomas were found in 62, 20, and 1 (not available in 7 patients). The most common TP53 mutations were R175H (n = 5) and R248Q (n = 4). Common co-mutated genes included KRAS (n = 15), ARID1A (n = 15), FGFR2 fusion (n = 14), IDH1 (n = 13), BAP1 (n = 10), CDKN2A (n = 9), and HER2 amplification (n = 8). Microsatellite unstable (MSI-H) tumors were found in 3 patients. The median tumor mutational burden was 2.5/Mb. Patients received front-line GC (n = 54), GC-nab-paclitaxel (GAP, n = 14), FOLFIRINOX (n = 3), and GC with targeted or trial therapy (n = 11, e.g. trastuzumab). mPFS with front-line therapy was 5.0 m (n = 90); it was 4.7 m with GC and 5.1 m with GAP. Patients who had co-mutated IDH1 or FGFR2 fusion had longer mPFS (9.5 and 6.9 m, respectively) than those who did not (n = 63, 3.7 m, p < 0.05) from front-line chemotherapy. mPFS after second-line FOLFOX (n = 17) and FOLFIRI (n = 10) was 2.1 and 1.9 m, respectively, and mPFS after third-line FOLFOX/FOLFIRI was 1.8 m (n = 8). The median overall survival (OS) of patients with co-mutated FGFR2, IDH1, or neither was 34.5, 22.0, and 13.1 m, respectively (p < 0.05). TP53-mutated BTC with mutations other than FGFR2/IDH1 did not show statistically significant difference in PFS or OS. Conclusions: Patients with TP53-mutated advanced BTC have shorter PFS than those without TP53 mutation in front and further-line settings. The presence of co-mutated FGFR2 or IDH1 is associated with improved PFS with chemotherapy (not FGFR/IDH1 inhibitors) and longer OS. Other co-mutations do not appear to have a survival benefit. It is crucial for clinicians to take into account the worse prognosis with TP53 mutation before starting front-line therapy in patients with advanced BTC and consider early clinical trial options.