Abstract <p>The effect of exogenous supplementation of glutathione (GSH: 0, 50 100 and 200 µM) on the growth and drought stress mitigation in soybean was evaluated. Drought (polyethylene glycol: 15% PEG) reduced growth parameters, chlorophyll synthesis, photosynthesis significantly and GSH supplementation proved beneficial in alleviating the decline in these parameters. The PEG treatment reduced the activity of δ-Amino levulinic acid dehydratase (δ-ALAD) and the synthesis of δ-amino levulinic acid (δ-ALA), chlorophylls and carotenoids; however, GSH treatments increased and also alleviated the decline caused by PEG (drought). The activity of Rubisco and the rate of photosynthesis increased by GSH treatment and the decline caused by drought was also mitigated in a concentration dependent manner. Drought stress increased chlorophyllase and lipoxygenase activity; however, GSH supplementation caused a significant decline in their activities. In addition, the increase in oxidative stress parameters (hydrogen peroxide and lipid peroxidation) due to drought was also lessened by the treatments of applied GSH. Exogenous treatment of GSH increased the activities of the antioxidant enzymes and also improved the accumulation of key non-enzymatic antioxidants (reduced glutathione, ascorbic acid and cysteine), thereby helping GSH-treated plants to cope the drought damage. Treatment of GSH resulted in increased proline and phenol in unstressed and the drought stressed plants, contributing to improved drought tolerance. Glutathione showed a beneficial impact on soybean growth and improved drought tolerance by regulating the key physio-biochemical parameters.</p>