Agronomic biofortification with selenium (Se) maybe employed to improve the nutritional value of food crops while increasing the plant’s tolerance to water deficit conditions. Although not essential for plants, Se may increase plant tolerance to water stress by boosting plants’ defence system activity. This study aimed to enrich common bean grains with Se and alleviate water deficit effects on common bean by applying Se to plants growing under greenhouse. Selenium was applied to soil at 0, 0.25, 0.5, 1.0, and 2.0 mg kg^–1, under irrigated and water-deficit conditions. Antioxidant enzyme activities (SOD, CAT, and APX), H₂O₂ content, gas exchange, and SPAD index were assessed in plant leaves, and Se and nutrient concentrations were determined in grains. Results showed that water deficit decreased photosynthetic rate, stomatal conductance, transpiration rate, and increased water use efficiency. Selenium did not influence SPAD index in leaves from pod formation to maturity stage but improved the plant defence system by decreasing H₂O₂ content. Increasing Se rates increased Se concentration in grains and leaves. At lower Se rates, mainly at 0.25 mg Se kg^–1, under water deficit, the activities of SOD, CAT, and APX reached their maximum values, and H₂O₂ content was minimum without reducing biomass production and nutrients accumulation. The highest Se rate (2 mg kg^–1) was detrimental, since it decreased biomass production and the plant defence system under water deficit. Conclusively, soil Se addition enriched common bean plants with Se and showed positive responses against water deficit when applied at lower rates.