The worldwide concern of ensuring a sustainable future for the coming generations has led to the idea of developing renewable functional materials. Cellulose, the most abundant natural biopolymer on earth is a remarkably low-cost material with excellent inherent properties. Nanocellulose is derived from different cellulosic sources in various forms which have excellent properties such as high surface area, crystallinity, mechanical strength, and tunable chemistry. Owing to these exciting features, cellulosic nanomaterials are integrated with other functional materials such as 2D graphitic materials to fabricate advanced hybrid materials which can be utilized as building blocks, robust carriers, scaffold components, and reinforcing materials. The exceptional synergies between cellulosic nanomaterials and graphene have resulted in significant innovations in this emerging field. In this critical review, an attempt has been made to critically discuss several key aspects related to processing such as solvent selection, homogeneous dispersion, and regeneration of nanocellulose-graphene based composites (NGCs). Special attention has been paid to the wide range of applications of NGCs in flexible electronic sensing, energy storage, biomedical, barrier and packaging, ultraviolet and electromagnetic shielding, thermal management, adsorption, and separation technologies. The major challenges in the respective fields have been highlighted, and the future prospects of NGCs toward developing advanced sustainable devices have also been outlined.