Radiotherapy is used in >50% of patients during the course of cancer treatment both as a curative modality and for palliation. However, radioresistance is a major obstacle to the success of radiation therapy and contributes significantly to tumor recurrence and treatment failure, highlighting the need for the development of novel radiosensitizers that can be used to overcome tumor radioresistance and, thus, improve the efficacy of radiotherapy. Previous studies indicated that resveratrol (RV) may sensitize tumor cells to chemotherapy and ionizing radiation (IR). However, the mechanisms by which RV increases the radiation sensitivity of cancer cells have not been well characterized. Here, we show that RV treatment enhances IR-induced cell killing in non-small cell lung cancer (NSCLC) cells through an apoptosis-independent mechanism. Further studies revealed that the percentage of senescence-associated β-galactosidase (SA-β-gal)-positive senescent cells was markedly higher in cells treated with IR in combination with RV compared with cells treated either with IR or RV alone, suggesting that RV treatment enhances IR-induced premature senescence in lung cancer cells. Comet assays demonstrate that RV and IR combined treatment causes more DNA double-strand breaks (DSBs) than IR or RV treatment alone. DCF-DA staining and flow cytometric analyses demonstrate that RV and IR combined treatment leads to a significant increase in ROS production in irradiated NSCLC cells. Furthermore, our investigation show that inhibition of ROS production by N-acetyl-cysteine attenuates RV-induced radiosensitization in lung cancer cells. Collectively, these results demonstrate that RV-induced radiosensitization is associated with significant increase of ROS production, DNA-DSBs and senescence induction in irradiated NSCLC cells, suggesting that RV treatment may sensitize lung cancer cells to radiotherapy via enhancing IR-induced premature senescence.