• FOXD3 is recruited to DNA double-strand breaks in a PARP1-dependent manner and interacts with PARP1.
• FOXD3 directly binds to MRE11 and promotes its recruitment to DSB sites, facilitating end resection.
• Inhibition of FOXD3 compromises homologous recombination repair and chromosome stability, sensitizing cancer cells to ionizing radiation.
• FOXD3 acts as a novel regulator of HR-mediated DSB repair and genome stability, independent of its transcription factor function.