Cuproptosis is a recently identified form of copper-dependent cell death. Here, we reveal that radiotherapy (RT) induces cuproptosis in cancer cells, independent of apoptosis and ferroptosis, and depletes lipoylated proteins and iron-sulfur (Fe-S) cluster proteins-both hallmarks of cuproptosis-in patient tumors. Mechanistically, RT elevates mitochondrial copper levels by upregulating copper transporter 1 (CTR1) and depleting mitochondrial glutathione, a copper chelator, thereby triggering cuproptosis. Integrated analyses of RNA sequencing (RNA-seq) from radioresistant esophageal cancer cells and single-cell RNA-seq from esophageal tumors of patients unresponsive to RT link radioresistance to the downregulation of BTB and CNC homology 1 (BACH1). This downregulation de-represses the expression of copper-sequestering metallothionein (MT) 1E/X, thereby mitigating cuproptosis and contributing to radioresistance. Copper ionophore treatment sensitizes radioresistant cancer cells and cell line- and patient-derived xenografts to RT by potentiating cuproptosis. Our findings unveil a link between RT and cuproptosis and inform a therapeutic strategy to overcome tumor radioresistance by targeting cuproptosis.