Today, biodiesel, a renewable, non-toxic and environmentally friendly fuel, is attracting increasing attention worldwide as an alternative to fossil fuel. In the present study, waste biomass-derived banana peel ash served as a heterogeneous catalyst for converting soybean oil into biodiesel at room temperature. The catalyst was well-characterized using IR, XRD, XRF, XPS, SEM, EDX, TEM, TGA and BET analysis techniques to assess its chemical composition, structure and morphology. The TEM-EDX, XPS and XRF analyses revealed the presence of several alkali metals and alkaline earth metals, which probably provide the basic sites for the transesterification reactions to produce biodiesel. A high biodiesel yield of 98.95% was achieved under the optimized reaction conditions. The catalyst has the advantage of being a waste material hence cost-free, easily prepared, biogenic, highly efficient, labor-effective and environmentally friendly; making it a potential candidate as a “green catalyst” for low cost production of biodiesel on the industrial scale.