This current work revealed a single-step fabrication of tungsten oxide nanoflakes (WO3 NFs) with the help of Terminalia arjuna bark extract. Bioactive phytoconstituents of T. arjuna bark extract were involved in the nucleation process and promoted the material crystalline growth in a particular direction. The as-prepared sample thermal decomposition was analyzed by TG/DTG. The as-prepared sample was annealed at 300 C for 2 h, and the annealed sample was characterized by UV-Vis-DRS, FTIR, Raman, XRD, SEM, EDX, and TEM. Synthesized WO3 samples showed a monoclinic phase of the flake-like structure with lengths of 25~230 nm and diameters of 25~120 nm. The WO3 NFs were evaluated against S. aureus and E. coli. Over 3 mg concentrations of WO3 NFs outperform the positive control in antibacterial activity. The pseudo-first-order kinetics of the WO3 NFs enhanced the photocatalytic performance of methylene blue (MB). These results prove that WO3 NFs have sustainable performance in antibacterial and MB degradation applications.