The aim of this study was to assess the impact of various levels of water stress, foliar application of proline and their interaction on the performance of mung bean [Vigna radiata L.]. A field experiment was carried out during the summer of 2025, in Najaf Governorate [Iraq], under a randomized complete block design with a split plot experimental design and three replications. Relevant main plot treatments were water depletion levels of 50, 60 and 70% of available water, with the subplots having four proline AtF treatments of 0, 50, 100 and 150 mg L⁻¹ foliar. In addition to leaf proline content and peroxidase [POD] activity, plant height, branch count, leaf area, pods plant-1, seeds pod-1, dry weight of the plants and yield of their seeds were measured. The results showed that increasing available water depletion from 50 to 70% caused a significant reduction in most growth traits and yield components; seed yield decreased from 1.64 to 0.69 t ha⁻¹, equivalent to a reduction of approximately 57.9%, while plant dry weight decreased from 58.25 to 40.18 g plant⁻¹. In contrast, foliar application of proline improved a number of the studied traits, and the concentration of 100 mg L⁻¹ was the most effective in terms of mean seed yield, which reached 1.43 t ha⁻¹ compared with 1.18 t ha⁻¹ in the control treatment, representing an increase of approximately 21.2%. The interaction between the two factors also showed that the response of mung bean to proline depended on the severity of water stress, with the 100 mg L⁻¹ treatment recording the highest yield of 1.89 t ha⁻¹ at 50% depletion, whereas the highest yield under severe stress was achieved by spraying at a concentration of 150 mg L⁻¹ and reached 0.77 t ha⁻¹. Increasing stress severity and proline treatments were accompanied by clear changes in proline accumulation and peroxidase activity, indicating the contribution of osmotic regulation and antioxidant defense mechanisms to the plant response to water deficit. The study concludes that foliar application of proline can serve as a supplementary physiological tool for alleviating water stress damage and improving mung bean performance.