Free radicals are triggered in human body by routine metabolic pathways which are highly reactive substance entangled in various physiological functions but excess production may impart with multitude diseases such as cancer, arthritis, inflammation and various neurodegenerative disorders. As a result, previous findings supported that various photochemical constituents present in natural plants exerts prominent role in defense mechanism against rate of excess free radicals’ production. The present study was carried out to investigate phytochemical composition, quantification studies and in vitro antioxidant potential of Justicia gendarussa (JG) various solvent extracts. JG belongs to the family Acanthaceace and used as traditional healers in various ailments. JG plant material was collected, dried, powdered and subjected for soxhlation to prepare ethanolic, ethyl acetate, aqueous and n-hexane extracts. Screening of Active constituents by various qualitative tests, estimation of total phenolic (TPC) and Total flavonoid content (TFC) and in vitro antioxidant potential of plant extracts were performed by DPPH, Lipid peroxidation, Nitric oxide and Superoxide radical scavenging methods. Present investigation reveals that, presence of flavonoids, phenols, amino acids, glycosides, cardiac glycosides, proteins, carbohydrates, alkaloids, steroids, terpenoids and tannins. TPC and TFC of ethanol extract were found to be 9.47 ± 0.0216 mg Gallic acid equivalent (GAE/g) and 97.6 ± 0.0342 mg Rutin equivalent/g (RUE/g). Among all the analyzed extracts ethanolic extract of JG possessed high radical neutralizing capacity and for DPPH (IC50 32µg/ml), Lipid Peroxidation (28 µg/ml), Nitric oxide (30 µg/ml) and superoxide anion radicals (39 µg/ml) respectively and found to be more effective as ascorbic acid (26 µg/ml) which was used as standard. Overall results of the study concluded that JG leaf extracts possess beneficial Phytoconstituents, high phenol and flavonoid contents and potential antioxidant activity, which could be a viable source of natural antioxidants for treating various degenerative disorders.