Municipal solid waste management has evolved into a promising approach to climate issues and to the growing energy demand in Tunisian cities. However, energy recovery from organic waste in the Metropolis of Tunis is still complex. This is due to the city's unpredictable economy, urbanization level, and population growth rates. So far, this unpredictability has constrained access to accurate data about organic waste. This has led to slow progress in harnessing organic waste for renewable energy production. This study focuses on the conversion of the city's organic waste to biogas as a local energy supply. The potential quantity of organic waste and its theoretical energy content were estimated based on a case study in four areas in the Metropolis encompassing 12 municipalities, official records, and literature reviews. The aim of this mixed method was to enhance data quality and optimize the long‐term viability of a small‐scale biogas plant in the city. The results show that the area generates a considerable amount of organic waste (55–66%) with an annual theoretical energy content of 224.18 GWh. The yearly financial gain from the 25.5 MW biogas plant could reach 40 352 400 USD. The estimated organic waste with its considerable potential energy content represents a significant renewable energy source in the Metropolis of Tunis. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd