Sustainable and clean energy conversion systems, which are one of the most demanding issues in the world, require the development of highly efficient catalysts. However, designing a catalyst with unique performance is the main challenge. The high cost of conventional catalysts of renewable energy conversion reactions (ECRs) containing scarce noble metals has inspired scientists to replace them with more practical composites. Extensive developments have been made in the application of carbon nanotubes (CNTs) in the energy transformation field because of their specific structures and excellent activity. This review will discuss the structural properties and the performance of composites prepared from CNTs, lignin, and polysaccharides. The applications of these composites in ECRs including electrocatalytic water splitting reactions, liquid fuel oxidation reactions, biological fuel cell reactions, proton exchange membrane (PEM), oxygen reduction reactions (ORRs), and CO₂ reduction reactions (CO₂RRs) will be presented in detail. This inclusive understanding will help readers and motivate researchers to develop composites containing CNTs and biopolymers with improved properties in the future.