The present study was aimed at determining phytochemical constituents with the aid of GC-MS technique and in vitro screening of pure methanol extracts of leaves from locally grown Amaranthus viridis plants for their antibacterial activity against human bacterial pathogens viz., Staphylococcus aureus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. The bioactive compounds present in the methanol extract fraction of A. viridis leaf were identified by GC-MS analysis which showed 50 peaks indicating the presence of fifty compounds. The results of the antibacterial activity proved the ability of the leaf extract of A. viridis to prevent the growth and survival of the test pathogens. Different bacterial species exhibited different sensitivities with variable extent towards the leaf extract. The order of activity against selected bacteria was Escherichia coli > Staphylococcus aureus > Bacillus cereus > Pseudomonas aeruginosa > Klebsiella pneumoniae. The methanol extract of A. viridis exerted maximum antibacterial activity against E. coli. The least activity was exhibited by P. aeruginosa and K. pneumoniae indicating their poor antibacterial activity. Medicinal plants are the backbone of traditional medicine and the antibacterial activity of plant extract is due to different bioactive substances in the extract with potential antimicrobial compounds.