Thermoelectric materials are emerging as pivotal components in the pursuit of sustainable energy solutions, offering the ability to directly convert waste heat into electricity. Among these, carbon-based nanocomposites (CBNCs) offer special benefits because of their cost-effectiveness, environmental friendliness, and adjustable characteristics. This chapter emphasizes how nanostructures work in concert to improve thermoelectric performance through phonon scattering, interface engineering, and quantum confinement. Key tactics for increasing energy conversion efficiency are examined, including adjusting the Seebeck coefficient, lowering thermal conductivity, and optimizing electrical conductivity. With an emphasis on their potential to lessen environmental effect, applications in waste heat recovery, portable power generation, and renewable energy integration are examined. Aspects of sustainability are rigorously examined, such as life cycle analysis, energy payback time, and the difficulties of practical application. Future directions highlight advancements in material design, optimization through the use of artificial intelligence, and commercialization routes. The revolutionary potential of CBNCs in developing thermoelectric technology and promoting a sustainable energy future is highlighted by this thorough review.