In the present study, silver (AgNPs) and gold (AuNPs) nanoparticles (NPs) have been prepared using the ethanolic extract of Nepeta leucophylla (NLe). This plant was considered owing to its richness in natural polyphenols and antioxidants that are well known for their reducing potential. Different techniques, such as UV (ultraviolet-visible spectrophotometer), FTIR (Fourier transform infrared radiation), and XRD (X-ray diffraction), were utilized for the characterization of NPs. The UV absorption peak was observed at 434 and 535 nm for NLe-AgNPs and NLe-AuNPs, respectively. FTIR suggested about the possible classes of biomolecules involved in the formation of metal NPs. XRD pattern confirmed the crystalline structure of gold and silver NPs and validated that the crystal structure under consideration is a face-centered cubic (FCC) pattern. High-resolution transmission electron microscopy (HR-TEM) images revealed that the NLe-AgNPs and NLe-AuNPs NPs were spherical in shape, with average diameter of 11.4 and 7.8 nm, respectively. The antioxidant potential was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, which revealed that NLe exhibited the highest antioxidant potential (79.37%) compared to synthesized metal NPs. Further, cytotoxic potential was evaluated using MTT assay against Hep G cell lines. The IC values were determined to be 5.97 µg/mL for NLe, 12.31 µg/mL for NLe-AgNPs, and 34.58 µg/mL for NLe-AuNPs, demonstrating their effectiveness in inhibiting cancer cell proliferation. The present results revealed that NLe may play a promising role in the cure of different deteriorative diseases. In future, more detailed studies based on animal model may be useful to support the present results and to evaluate further health benefits of NLe.