Transesterification has become the prominent methodology for biodiesel production, compared to other alternatives such as pyrolysis, direct-blending, and microemulsion techniques. This study utilized waste cooking oil as a precursor for biodiesel production, representing an eco-friendly approach to the sustainable generation of renewable energy. The catalyst plays a crucial role in accelerating the reaction rate and improving yield during the transesterification process. In this research, ZnO nanoparticles synthesized using goat fecal matter (GFM) extract were employed as a reducing agent for zinc sulfate. The ZnO nanoparticles act as a heterogeneous catalyst, facilitating easier separation and reusability compared to homogeneous catalysts. The waste cooking oil (WCO) to biodiesel conversion was achieved at a reaction temperature of 65 °C, with a reaction time of 285 min, and a methanol-to-oil ratio of 9:1, using 0.9375 wt% catalyst concentration. A conversion rate of 78.92% from oil-to-biodiesel conversion was accomplished with ZnO nanocatalyst, while maintaining efficient catalytic properties over four reaction cycles. The ZnO nanoparticles were characterized using various techniques. Scanning Electron Microscopy (SEM) examined the morphological properties of the synthesized nanoparticles. Fourier-Transform Infrared Spectroscopy (FT-IR) provided information regarding the sample’s composition, purity, and the successful synthesis of ZnO nanoparticles. Analysis using Transmission Electron Microscopy (TEM) showed the presence of irregular hexagonal ZnO nanoparticles with a mean particle size of 11.20 ± 2.81 nm, confirming their nanoscale nature and good crystallinity. An 81.09% degree of crystallinity was observed in X-ray diffraction analysis. Finally, the primary constituent of biodiesel, fatty acid methyl esters (FAME), was analyzed using Gas Chromatography-Mass Spectrometry (GC-MS).