A simple, facile, moist-heating (, autoclave), one-step procedure for EGCG-mediated biosynthesis of narrow-size magnetic iron oxide (α-FeO) nanoparticles (EGCG-MINPs) was developed. The influence of pH of the reaction mixture over the size distribution of as-synthesized EGCG-MINPs was investigated systematically by employing UV-visible (UV-vis) spectroscopy and dynamic light scattering (DLS)-based hydrodynamic size, surface charge (zeta-potential), and polydispersity index (PDI). The FE-SEM, TEM, and XRD characterizations revealed that the EGCG-MINPs synthesized at pH 5.0 were in the size range of 6.20-16.7 nm and possess well-crystalline hexagonal shaped nanostructures of hematite (α-FeO) crystal phase. The role of EGCG in Fe ion reduction and EGCG-MINP formation was confirmed by FTIR analysis. The VSM analysis has revealed that EGCG-MINPs were highly magnetic nanostructures with the hysteretic feature of saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) as 33.64 emu/g, 12.18 emu/g, and 0.33 Oe, respectively. Besides, significant ( < 0.001) dose-dependent (250-1000 μg/mL) antibacterial and antibiofilm activities against the NDM-1-producing Gram-negative (AK-33), (AK-65), (AK-66), and (AK-67) bacterial isolates warranted the as-synthesized EGCG-MINPs as a promising alternative for clinical management of chronic bacterial infections in biomedical settings. In addition, molecular docking experiments revealed that compared to free Fe and EGCG alone, the EGCG-MINPs or Fe-EGCG complex possess significantly high binding affinity toward HSA and hence can be considered as promising biocompatible nanodrug carriers in drug delivery systems.