This paper addresses the use of agro-industrial residue as a promising heterogeneous catalyst for the efficient production of biodiesel. That is, CaO-rich Sugarbeet agro-industrial waste (smashed down to nano-size) shows superb catalytic activity for biodiesel production via transesterification process employing sunflower oil and methanol. Physicochemical properties of the proposed catalyst are probed by TGA–DTG, XRF, XRD, FT-IR, SEM, BET, and CO2-TPD techniques. Biodiesel conversion (%) of Ca. 93% is achieved under the optimal conditions (catalyst loading of 1 wt%, methanol/oil molar ratio of 4.5:1, refluxed at 75 °C for 60 min). The relatively short reaction time indicates the enhanced kinetics of the process using the proposed agro-industrial residue which imparts its economic feasibility. Also, the proposed CaO-rich residue can be reused twice while retaining its catalytic activity. The thus-produced biodiesel fuel compiles the ASTM D6751 and EN-14214 specifications.