We developed a computational method to infer the complementarity determining region 3 (CDR3) sequences of tumor infiltrating T-cells in 9,142 RNA-seq samples across 29 cancer types. We identified over 600 thousand CDR3 sequences, including 15% with full-length. CDR3 sequence length distribution and amino acid conservation, as well as variable gene usage of infiltrating T-cells in many tumors, except brain and kidney cancers, resembled those in the peripheral blood of healthy donors. We observed a strong association between T-cell diversity and tumor mutation load, and predicted SPAG5 and TSSK6 as putative immunogenic cancer/testis antigens in multiple cancers. Finally, we identified 3 potential immunogenic somatic mutations based on their co-occurrence with CDR3 sequences. One of them, PRAMEF4 F300V, was predicted to bind strongly to both MHC-I and MHC-II, with matched HLA types in its carriers. Our analyses have the potential to simultaneously identify immunogenic neoantigens and the tumor-reactive T-cell clonotypes.