T cell immunoglobulin mucin-3 (TIM-3) is expressed on the surface of most immune cells and is involved in anti-tumor immunity. In recent years, diagnoses and therapies based on the TIM-3 target have advanced substantially in clinical trials. In this review, we summarized the progress of TIM-3 as a biomarker in the field of diagnosis and prognosis of cancer. In the peripheral blood of cancer patients, the expression level of TIM-3 on T cells is significantly higher than that of control samples, which can be a physiological indicator of cancer. Moreover, in the cancer tissue of patients, the high expression level of TIM-3 on tumor-infiltrating T cells is negatively correlated with relapse-free survival time, which can act as a promising prognostic marker. In conclusion, the TIM-3 is a promising biomarker for the diagnosis and prognosis of cancer.