The increasing global demand for sustainable fuels has greatly boosted research into converting waste cooking oil (WCO) into biodiesel, positioning it as a renewable alternative to conventional fossil diesel. This study thoroughly investigates the transesterification of WCO using a calcium oxide (CaO) heterogeneous catalyst. The research includes kinetic modelling, process simulation, and an extensive environmental assessment to provide a comprehensive understanding of the process. The process conditions set for this study included a temperature range of 30°C to 70°C, with methanol-to-oil molar ratios varying from 6:1 to 14:1. Reaction times ranged from 60 to 100 minutes, and a catalyst loading of 3 wt.% CaO was used. To characterise the reaction kinetics effectively, a pseudo-first-order kinetic model was utilised. In this investigation, the activation energy (Ea) was determined to be 37.16 kJ·mol⁻¹, indicating an energetically favourable reaction pathway under the moderate operating conditions used. The validation of the kinetic model was conducted using ChemCAD simulation, which accurately predicted a maximum conversion rate of 98.96% at a methanol-to-oil molar ratio of 6:1 at 70°C. This confirms the strong catalytic efficiency and practical reusability of CaO in the transesterification process. Additionally, a cradle-to-gate Life Cycle Assessment (LCA), focusing on Global Warming Potential (GWP), showed that producing one tonne of biodiesel results in emissions of only 640 kg CO₂-equivalent. This figure is approximately 80% lower than the typical emissions of 3200–3500 kg CO₂-equivalent associated with petroleum diesel production. The analysis revealed that methanol synthesis and process energy consumption were the primary contributors to overall emissions, while the environmental impacts associated with catalyst usage and WCO collection remained minimal. In conclusion, the findings of this study demonstrate that transesterification of WCO catalysed by CaO is not only technically feasible but also environmentally advantageous, offering a promising pathway towards sustainable low-carbon fuel production and effective waste valorisation. This research aligns with the United Nations Sustainable Development Goal 12 (Responsible Consumption and Production), as it promotes sustainable practices and reduces waste by converting WCO into biodiesel.