Drought and salinity are the major abiotic factors that induce water stress in plants, consequently lowering crop productivity. Oman is considered an arid region, where the limited rainfall, high temperature, and overusing of aquifers water influence soil salinization and drought. Cowpeas (Vigna unguiculata) plants can tolerate poorly fertilized soil and harsh environmental conditions, including drought and salinity. The phytohormone melatonin (MT) is produced in high concentrations by plants under environmental stresses and it acts as an antioxidant. The current study aimed to investigate the effect of MT on cowpea plants' tolerance to salt and drought stress. The optimization experiment used salt stress (150 mM NaCl), in which cowpeas were grown for one week, then exposed to salt stress for two weeks, and foliar application of different MT concentrations (25-400 µM). Cowpeas seedlings were exposed to two drought conditions (moderate and severe) for four weeks. Various growth and stress tolerance parameters were measured upon treating the plants with MT. This includes photosynthetic characteristics, chlorophyll pigments, and cowpea's antioxidant defense capacity changes in the enzymatic and nonenzymatic systems. The results showed that A 300 µM concentration was the most effective concentration of MT that promotes salt and drought tolerance of cowpea. Plant height and leaf area were significantly enhanced by MT treatment by 32.36% and 39.36%, respectively, compared to salt-stressed cowpeas. MT supplementation raised stomatal conductance (gs) and photosynthesis rate (A) by 60% and 29.4%, respectively, compared to salt stressed cowpeas. Similarly, MT promoted plant height and leaf area under severe drought stress by 13.63% and 18.75 respectively. Moreover, it increased gs and A by 56.6% and 29.5%, respectively. In addition, MT raised the enzymatic antioxidant activity (SOD and CAT) and osmolytes (proline and flavonoids), reduced hydrogen peroxide levels, and regulated Na+ accumulations in leaves in stressed cowpeas plants. Overall, the foliar application of MT enhanced plant growth and photosynthesis in salt and drought-stressed seedlings and strengthened the antioxidant system. This study can mediate further research on cowpea plants in the Omani environment.