Nanobiotechnology has become a newly evolving field of interest in biomedical applications due to its biocompatibility and non-toxic nature towards the environment. Metal and metal oxide nanoparticles have been widely used as an antibacterial agent due to the emergence of antibiotic resistant pathogens, which leads to the outbreak of infectious diseases. In the present paper, biogenic synthesis of magnesium oxide (MgO) nanoflakes is reported by using Bauhinia purpurea leaf extract through alkaline precipitation method along with its detailed characterization. The average size of synthesized nanoflakes was found to be around 11 nm. Electron microscopy was used to investigate the morphology of the MgO nanoflakes. Additionally, the presence of antioxidants, phenolics and flavonoids in B. purpurea leaf extract has been studied by using different assays, which suggested the efficacy of leaf extract as a potential reducing agent for MgO nanoflakes synthesis. Antibacterial activity of synthesized MgO nanoflakes was investigated against Staphylococcus aureus, a gram positive bacteria known to cause various infections in humans. Results suggested the high efficacy of MgO nanoflakes as a potential antibacterial agent against S. aureus at meager dose size (250 μg/ml) and possible mode of action was investigated through surface morphology analysis of bacterial cells by field emission scanning electron microscopy.