The present study delves into an eco-friendly and scalable method for creating zinc oxide (ZnO) nanoparticles using extract from Piper betle leaves. By harnessing the natural bio-reductive and capping abilities of the phytochemicals found in P. betle, the ZnO nanoparticles formed a hexagonal wurtzite structure, with an average crystallite size of about 20.3 nm, as confirmed by XRD analysis. The UV–Visible spectroscopy results showed a notable blue shift in absorption, leading to an estimated band gap of 4.10 eV, which is linked to quantum confinement effects. FTIR spectra confirmed the presence of biomolecules on the surface, while SEM imaging displayed quasi-spherical polycrystalline particles with some aggregation. To assess the photocatalytic potential, we evaluated the degradation of methylene blue (MB) dye under UV light, where the Piper betle–ZnO catalyst achieved over 90% degradation efficiency in just ~80 minutes, with a pseudo-first-order rate constant of 0.0342 min^-1. These results highlight the collaborative role of P. betle's phytoconstituents in shaping the nucleation, growth, and surface chemistry of ZnO nanoparticles, which enhances their ability to absorb light and separate charge carriers. This green approach presents a promising strategy for developing effective photocatalysts aimed at cleaning up wastewater.