In this work, the use of a banana peel-derived basic heterogeneous catalyst is investigated for producing biodiesel from sunflower oil. The catalyst is produced by treating dried banana peels at 700 °C under normal atmosphere for 4 h. The reaction parameters were optimized by varying the methanol-to-oil molar ratio (MOMR) and the catalyst-to-oil ratio (CTOR). The highest conversion of sunflower oil to biodiesel (99.4%) was attained after a reaction time of 90 min using an MOMR of 9:1, a catalyst loading of 4 wt%, and a stirring rate of 300 rpm. The catalyst demonstrated good stability, with a yield of 99.4% (±0.28%) obtained over three consecutive runs. No active phase loss was observed during the consecutive reactions, as confirmed by the leaching test. The physical and chemical properties of the formed biodiesel were in good accordance with the American Society for Testing and Materials (ASTM) standards. The kinetic study allowed for the determination of the activation energy (Ea = 58.1 kJ/mol) and pre-exponential factor (A = 7.4 × 10⁷ min⁻¹) of the catalyzed reaction. Additionally, the valorization of waste cooking oil (WCO) (a second-generation feedstock oil) using the waste banana peel-derived catalyst under optimum reaction conditions achieved a yield of 99.1% (±0.14%).