The current study focuses on the phytochemical characterization and biological activity of phenolic compounds derived from leaves of Moringa oleifera Lam. (Moringaceae) in the Tabelbala area (Bechar, Algeria). For a concentration of 1 mg/ml, the antioxidant tests revealed that the different extracts have a good reducing activity, with the tannin extract having the highest percentage of free radical inhibition (DPPH: 94%) compared to the n-butanolic extract (92%) and the ethyl acetate extract (88%). Furthermore, the tannin extract and the n-butanolic fraction of the flavonoids of the examined leaves showed significant antioxidant activity compared to ascorbic acid used as a reference (IC50 = 0.05 ± 0.14 mg/ml), with IC50 values of 0.07 ± 0.79 mg/ml for tannins and 0.0823 ± 0.25 mg/ml for the n-butanolic extract. In addition, the ferric reduction antioxidant power (FRAP) test reveals that all the tested extracts have a significant reduction power. The different selective extracts showed strong antimicrobial activity against nine pathogenic microbial strains: Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (ATCC 13883), Citrobacter freundii (ATCC 29212), Acinetobacter baumannii (ATCC 19606), Bacillus cereus (ATCC 11778), Staphylococcus aureus (ATCC 25923), Enterococus faecalis (ATCC 13045), and Candida albicans, where the ethyl acetate fraction has a higher antibacterial activity than n-butanolic and tannin extract, with the zone of inhibition diameters ranging from 11 to 23 mm and have minimum inhibitory concentrations (MIC) between 0.39 and 3.125 mg/ml. These findings give scientific support for the plant’s traditional use, highlighting the value of traditional medicines in the treatment of many diseases.