Tumor resistance to chimeric antigen receptor T cell (CAR-T) and, in general, to adoptive cell immunotherapies (ACTs) is a major challenge in the clinic. We hypothesized that inhibiting the tumor drivers' methyltransferases EZH2 and EZH1 could enhance ACT by rewiring cancer cells to a more immunogenic state. In human B cell lymphoma, EZH2 inhibition (tazemetostat) improved the efficacy of anti-CD19 CAR-T by enhancing activation, expansion, and tumor infiltration. Mechanistically, tazemetostat-treated tumors showed upregulation of genes related to adhesion, B cell activation, and inflammatory responses, and increased avidity to CAR-T. Furthermore, tazemetostat improved CAR- and TCR-engineered T cell efficacy in multiple liquid (myeloma and acute myeloid leukemia) and solid (sarcoma, ovarian, and prostate) cancers. Lastly, combined EZH1/EZH2 inhibition (valemetostat) further boosted CAR-T efficacy and expansion in multiple cancers. This study shows that EZH1/2 inhibition reprograms tumors to a more immunogenic state and potentiates ACT in preclinical models of both liquid and solid cancers.