Magnesium oxide nanoparticles (MgONPs) synthesized by efficient green approach have unique physiochemical properties. In this study, MgONPs are synthesized with bract extract of Musa acuminate, an agro waste. The surface plasmon resonance at 450 nm in UV spectrum and FTIR peaks at 601 and 890 cm−1 confirmed the presence of MgONPs. XRD pattern revealed high crystallinity of the nanoparticles with an intense orientation peak at 111, and the size was 13 nm. The particles were spherical with an average size of 24.85 nm. The elemental percentage of magnesium and oxygen were 68.55% and 31.45%. MgONPs had antibacterial activity against Bacillus subtilis, Escherichia coli, Vibrio harveyi, Vibrio parahemolyticus, and Staphylococcus aureus with MIC, 6 μg/mL. The IC50 value for MCF‐7 cell was 113.56 μg/mL, and the normal cell line was 785.69 μg/mL. The NPs also exhibited hemolytic features in a dose‐dependent manner. The MgONPs exhibited photocatalytic degradation of methyl violet, CBB G‐250, and malachite green in 60 min duration. MgONPs had promising antibacterial, cytotoxic, hemolytic, photocatalytic, and seed germination activity. They have the potential to serve as an additive in a variety of biological applications.