Gallbladder cancer is a highly aggressive malignancy with an extremely poor prognosis. Germline BRCA1 mutation in gallbladder cancer is very rare. Herein, we present a case of a 73-year-old Asian patient diagnosed with lymph nodes and peritoneal metastases just two months after surgery for primary gallbladder cancer. The patient had a past history of early-stage breast cancer and received a left radical mastectomy 27 years ago. Next-generation sequencing (NGS) was performed as the patient refused to receive systemic chemotherapy. According to NGS result of germline BRCA1 mutation, the patient was administered first-line Olaparib and obtained a progression-free survival of about 6 months. Furthermore, we briefly summarized the current targeted treatment of gallbladder cancer. To the best of our knowledge, this is the first report of germline BRCA1 p. S451Lfs*20 mutation and first-line Olaparib treatment in a metastatic gallbladder cancer patient. As a highly heterogeneous and aggressive malignancy, we suggest making clinical decisions according to a precision medicine concept based on gene sequencing in advanced gallbladder cancer.