Glutathionylation involves reversible protein cysteine modification that regulates the function of numerous proteins in response to redox stimuli, thereby altering cellular processes. Herein we developed a selective and versatile approach to identifying glutathionylation by using a mutant of glutathione synthetase (GS). GS wildtype catalyzes coupling of gamma Glu-Cys to Gly to form glutathione. We generated a GS mutant that catalyzes azido-Ala in place of Gly with high catalytic efficiency and selectivity. Transfection of this GS mutant (F152A/S151G) and incubation of azido-Ala in cells efficiently afford the azide-containing glutathione derivative, gamma Glu-Cys-azido-Ala. Upon H2O2 treatment, clickable glutathione allowed for selective and sensitive detection of glutathionylated proteins by Western blotting or fluorescence after click reaction with biotin-alkyne or rhodamine-alkyne. This approach affords the efficient metabolic tagging of intracellular glutathione with small clickable functionality, providing a versatile handle for characterizing glutathionylation.