A novel multi-component route for the synthesis of spiro-benzimidazoquinazolinones has been developed under microwave irradiation. It involves a one-pot three-component reaction of acenaphthoquinone or isatin, 1,3-diketone and 2-aminobenzimidazole in ethanol at 180 W and 160 °C temperature. An attractive feature of this method is the mild conditions with operational simplicity. The computational studies provide insight into the mechanistic aspects of the reaction.