Immune checkpoint inhibitors (ICIs) are innovative immunotherapeutic agents used to treat various types of cancer by enhancing T-cell-mediated antitumor activity. These agents have distinct adverse events, known as immune-related adverse events, which can affect multiple organ systems and typically occur within a year after initiating ICI therapy. Another concern regarding ICI therapy is the potential development of T-cell lymphomas due to prolonged activation of T-cell activity. We report the case of a 56-year-old female who was treated with nivolumab for metastatic melanoma for over seven years and subsequently developed concurrent angioimmunoblastic T-cell lymphoma and ICI-related cholangitis. This case highlights the importance of careful monitoring for the emergence of late-onset T-cell lymphoma in patients undergoing long-term ICI therapy.