To make the biodiesel competitive with petroleum diesel, cheap and abundant materials can be utilized as a catalyst and waste oils can be used as resources. In this research study, the potential of waste chicken eggshells was used as a catalyst to produce biodiesel from the rendered chicken fats (RCF). The calcium methoxide catalyst was prepared by calcining the waste eggshells at 900 °C in air for 4 h followed by treatment with methanol under reflux condition. The physico-chemical properties of the prepared catalyst were characterized using the X-ray diffraction (XRD) analysis, Brunner-Emmet-Teller (BET), field emission scanning electron microscopy (FE-SEM), and temperature programmed desorption of carbon dioxide (CO2-TPD). Two-step process including, esterification and transesterification were employed to convert the RCF to fatty acid methyl ester (FAME). Esterification pretreatment with ferric sulfate successfully reduced 75.1% of the FFA content in RCF which enables high biodiesel production. Under the optimal reaction condition, the highest conversion of biodiesel was found to be 90.04% at 1:15 oil to methanol molar ratio, 3 wt% catalyst loading, and 2 h reaction time at 65 °C. The catalyst was successfully used for 4 consecutive cycles with less than 2 mg/kg of Ca was detected in the product.