Cellulose and chitosan are the most widely accepted natural biopolymers for the fabrication of a wide spectrum of bio-composites. The various functional groups present in cellulose and chitosan allow its chemical and physical transformations, which is favorable to advanced applications. Both cellulose- and chitosan-based materials show various advantages such as biodegradability and biocompatibility. In addition, these composites have the flexibility to adapt to various physical and chemical transformations. The incorporation of highly abundant copper and iron in the form of nanostructures with these biopolymers results in environmentally friendly, biodegradable bio-composite. The utilization of copper/iron-based bio-nanocomposites with cellulose and chitosan is forecasted to have a significant impact on various fields including the medical field, packaging applications, sensors, antibacterial, antifungal, catalysis, and water purification. The present chapter brings up a comprehensive compilation of the existing and future applications of copper- and iron-based bio-nanocomposites with cellulose and chitosan in different fields.