YTH domain–containing family protein 1 (YTHDF1), a reader of N6-methyladenosine (m 6 A), has been implicated in regulating RNA metabolism in the cytosol. Here, we report a role of YTHDF1 within the nucleus in response to genotoxic stress. Upon radiation, YTHDF1 is phosphorylated at serine-182 in an ataxia telangiectasia and Rad3-related–dependent manner. This phosphorylation inhibits exportin 1–mediated nuclear export of YTHDF1, resulting in its accumulation within the nucleus. Nuclear YTHDF1 enhances the binding capacity of serine- and arginine-rich splicing factor 2 to a group of m 6 A-modified exons, leading to increased exon inclusion. Specifically, YTHDF1 promotes splicing and expression of DNA repair genes, such as BRCA1 and TP53BP1 , thereby mitigating excessive DNA damage. Depletion of YTHDF1 sensitizes cancer cells to radiation treatment. Together, our study reveals a crucial role of YTHDF1 in m 6 A-mediated messenger RNA splicing in the DNA damage response, proposing it as a potential target for radiation therapy.