Herein, Zinc Oxide nanoflowers (ZnONFs) with low cost, non‐hazardous and renewable phytochemicals from plant (Thlaspi arvense) extract were synthesized via facile method under controlled optimized experimental conditions. The as‐fabricated Zinc Oxide nanoflowers were comprehensively characterized by UV–visible spectroscopy, Fourier Transform infrared spectroscopy, X‐ray diffraction, Scanning electron microscopy, High‐resolution transmission electron microscopy, and Energy dispersive spectroscopy techniques. The bio‐fabricated Zinc Oxide nanoflowers performed an admirable potential activity against Gram‐negative bacterium (Escherichia coli) and significantly inhibited its growth, due to an intracellular generation of reactive‐oxygen‐species. The photocatalytic performances of as bio‐synthesized Zinc Oxide nanoflowers were also tested by reducing 4‐nitrophenol and methylene blue. The superior photocatalytic activities of Zinc Oxide nanoflowers are attributed to the high surface area, efficient photogenerated electron and hole separation owing to the capped plant moieties. The as‐synthesized Zinc Oxide nanoflowers by green method exhibited a significant antibacterial activity and efficient photocatalytic performances. This synthetic strategy will open a new window for the fabrication of nanomaterial with effective removal of wastewater contaminants and pathogens.