The development of environmentally benign and efficient strategies for synthesizing biologically important heterocycles remains a pivotal challenge in contemporary organic chemistry. Among these, benzimidazole derivatives represent a class of vital heterocyclic compounds with diverse and significant pharmacological applications. This underscores the necessity for advancing sustainable and catalytic methodologies to achieve their efficient and selective synthesis. In this regard, a novel water-assisted strategy has been developed for the synthesis of substituted benzimidazole scaffolds through the reaction of 2-haloanilines, sodium azide, and aldehydes under ultrasound irradiation, catalyzed by a CuO-decked reduced graphene oxide (rGO) nanocomposite in aqueous medium. The CuO-rGO nanocomposite was synthesized via a one-pot chemical route and thoroughly characterized using various analytical techniques. Compared to conventional methods, the CuO-rGO nanocomposite exhibited a 20-fold increase in catalytic activity under ultrasound irradiation. The synergistic effect between water, the catalyst’s functionalities, and ultrasound irradiation played a pivotal role in the successful synthesis of the desired products. Furthermore, the catalyst could be easily recovered by centrifugation and reused successfully for up to eight cycles without a loss in activity.