Depletion of non-renewable energy sources and exhaustion of fossil fuels create an urgency to convert solid biowaste into benign materials. In this present work, waste Pholas orientalis shells were transformed into heterogeneous catalyst via calcination and calcination-impregnation-activation treatment, yielding POS 900 and POS 900–600 catalysts, respectively. The catalysts were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and N2 adsorption-desorption analysis and evaluated in the transesterification of waste cooking oil (WCO) at reaction conditions of 5 wt.% catalyst loading, 15:1 (methanol:oil v/v) at 65 ̊C for 1 h. The presence of CaO, Ca(OH)2 and CaCO3 were identified through the FTIR and XRD studies. The BET surface area increases in the following trend POS 900–600 (12.93 m2/g) > POS 900 (2.18 m2/g) > commercial CaO (1.86 m2/g). Biodiesel production was maximum (96.16%) over POS 900–600 while 92.30% and 73.54% were registered for POS 900 and commercial CaO catalysts, respectively. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of the bio-oil confirmed the existence of fatty acid methyl ester (FAME) compounds such as hexadecanoic acid methyl ester (methyl palmitate), 8-octadecanoic acid methyl ester (methyl stearate) and tetradecanoic acid methyl ester (methyl myristate). ASTM D664 recorded the acid value of the biodiesel over POS 900–600 and POS 900 as 0.12 and 0.27 mg KOH/g. POS 900–600 was stable during the regeneration studies, even after five consecutive cycles. To conclude, this research confirmed the successful conversion of waste Pholas orientalis into a competent and reusable catalyst for biodiesel production.