This paper intends to explore the most affordable and environmentally friendly method for the synthesis of biodiesel. Substitute fuel is presently a significant topic all over the world, attributable to the efforts of reducing global warming, which is the result arising from the combustion of petroleum or petrol diesel fuel. Due to its advantages of being renewable and environmentally friendly, biodiesel production has the potential to become the major substitute of petrol diesel fuel. Biodiesel is non-toxic, biodegradable, is produced from renewable sources, and contributes a small amount of greenhouse gas (e.g., CO₂ and SO₂) emissions to the atmosphere. Research has established that one of the key obstacles to the commercialization of biodiesel is the high price of biodiesel production due to the shortage of suitable raw materials. However, waste-cooking-oil (WCO) is one of the most cost-effective sources of biodiesel synthesis, and can practically minimize the raw material cost. The research was carried out to produce biodiesel from waste cooking oil in order to reduce the cost, waste, and pollution associated with biodiesel production. The application of a microwave heating system towards enhancing the production of biodiesel from waste cooking oil has been given little consideration in the preceding research, particularly with the application of eggshell as a heterogeneous catalyst. However, the tentative results in this study show significant performance in terms of biodiesel production, as follows: (1) the increasing of the reaction time from 120 to 165 min considerably increased the biodiesel production, which declined with a further rise to 210 min; (2) the results of this study reveal that a methanol-to-oil molar ratio of nine is appropriate and can be used for the best production of biodiesel; (3) the production of biodiesel in this study demonstrated a significant increase in response to the further increasing of power; (4) a 120 min response time, a ratio of 9:1 methanol-to-oil molar fraction, 65 °C temperature; (5) and 5 wt % catalyst were found to be the most ideal reaction conditions during this study. In summary, recycled eggshell was re-used as a suitable catalyst to produce new biodiesel from waste cooking oil, applicable to diesel engines.