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.