The timing of radiation after mechanical injury such as in the case of surgery is considered a clinical challenge because radiation is assumed to impair wound healing. However, the physiological responses and underlying mechanisms of this healing impairment are still unclear. Here, we show that mechanical injury occurring before ionizing radiation decreases radiation-induced cell damage and increases cell repair in normal fibroblasts but not tumor cells in vitro and in vivo. At the molecular level, mechanical injury interrupts focal adhesion complexes and cell-cell cadherin interactions, transducing mechanical signals into intracellular chemical signals via activation of the phosphatidylinositol 3-kinase (PI3K), Akt, and glycogen synthase kinase 3 beta (GSK-3β) pathways. We show that subsequent nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and β-catenin strengthen the stemness, antioxidant capabilities, and DNA double-strand break repair abilities of fibroblasts, ultimately contributing to increased radioresistance. Our findings demonstrate that mechanical injury to normal fibroblasts enhances radioresistance and may therefore question conventional wisdom surrounding the timing of radiation after surgery.