Oncolytic viruses (OVs), known for their cancer-killing characteristics, overturn tumor-associated defects in antigen presentation through the MHC class I pathway and induce protective neo antitumor CD8 T cell responses. Nonetheless, whether OVs shape the tumor MHC-I ligandome remains unknown. Here, we investigated if an OV induces the presentation of novel MHC I-bound tumor antigens (termed tumor MHC-I ligands). Using comparative mass spectrometry (MS)-based MHC-I ligandomics, we determined differential tumor MHC-I ligand expression following treatment with oncolytic reovirus in a murine ovarian cancer model. In vitro we found that reovirus induces the presentation of tumor MHC-I ligands in cancer cells. Concurrent multiplexed quantitative proteomics revealed that the changes in tumor MHC-I ligand presentation were mostly independent of reovirus-induced alterations of their source proteins. In an in vivo model, tumor MHC-I ligands were induced by reovirus which were detectable not only in tumor tissues but also the spleens (a source of antigen-presenting cells) of tumor-bearing mice. Most importantly, therapy-induced MHC-I ligands contained biologically active epitopes that stimulated antigen-specific IFNgamma response in antitumor CD8 T cells. These data show that the therapy-induced MHC-ligands shape underlying neo antitumor CD8 T cell responses, and advocate for the consideration of the 'induced' MHC-I ligands in promoting the efficacy of OV-based cancer immunotherapies.