The advent of immune checkpoint inhibitors (ICIs) has ushered in a new era in the field of cancer therapy, allowing for the potential of prolonged life in patients with metastatic illness, and offering novel therapeutic applications in the early stages of the disease. Immune checkpoint inhibitors may reinstate the immune system’s capacity to combat cancer cells and halt their proliferation by obstructing these proteins. The validity of these results is supported by sufficient clinical trial evidence, and now, many immune checkpoint inhibitors have been authorized by the FDA and are available on the market for the treatment of different kinds of malignancies. They work by inhibiting checkpoint proteins such as CTLA-4, PD-1, PD-L1, etc. They may be used alone or in conjunction with other cancer therapies, such as surgery, radiation, or chemotherapy. In this article, we offer a comprehensive review of these inhibitors and their significance as biomarkers, immune-related bad effects, and their relevance in clinical research for the treatment of different types of malignancies. Additionally, we discuss some potential future possibilities.