RNA methylation is an important regulatory process to determine immune cell function but how it affects the anti-tumor activity of CD8 T cells is not fully understood. Here we show that the N6 -methyladenosine (m6 A) RNA reader YTHDF2 is highly expressed in early effector or effector-like CD8 T cells. We find that YTHDF2 facilitates nascent RNA synthesis, and m6 A recognition is fundamental for this distinctively nuclear function of the protein, which also reinforces its autoregulation at the RNA level. Loss of YTHDF2 in T cells exacerbates tumor progression and confers unresponsiveness to PD-1 blockade in mice and in humans. In addition to initiating RNA decay that is necessary for mitochondrial fitness, YTHDF2 orchestrates chromatin changes that promote T cell polyfunctionality. YTHDF2 interacts with IKZF1/3, which is important for sustained transcription of their target genes. Accordingly, immunotherapy-induced efficacy could be largely restored in YTHDF2- deficient T cells through combinational use of IKZF1/3 inhibitor lenalidomide in a mouse model. Thus, YTHDF2 coordinates epi-transcriptional and transcriptional networks to potentiate T cell immunity, which could inform therapeutic intervention.