Perennial ryegrass (Lolium perenne) is an important forage and turfgrass species that is sensitive to drought stress. The objective of this study was to investigate whether gamma aminobutyric acid (GABA) may play a role in promoting drought tolerance in grass species. GABA was exogenously applied as a foliar spray at the rate of 50 or 70 mm to perennial ryegrass ‘CSI’ under well-watered or drought-stressed conditions in a controlled-environment growth chamber. The effect of GABA on the growth physiology, drought stress response, antioxidant activity, and lipid peroxidation of perennial ryegrass exposed to drought stress was measured. GABA-treated perennial ryegrass exposed to drought stress had higher relative water content (RWC), turf quality, and peroxidase activity and lower wilt rating, canopy temperature depression, electrolyte leakage, and lipid peroxidation compared with untreated plants. GABA application had no significant effect on the activity of superoxide dismutase and catalase under well-watered and drought conditions. GABA application at 50 mm was found to be more effective in alleviating drought stress damage in perennial ryegrass. The results from this study suggest that GABA mitigated drought stress damage in perennial ryegrass by maintaining higher RWC and membrane stability.