Nanogenerators are the newest edition in the field of Renewable energy devices. These devices’ applications range from energy harvesting from mechanical force to driving advanced sensors and electronic devices. There are many challenges in the fabrication process like the selection of electrodes, materials, type of contact wire, etc., which significantly affects the output power. Flexible nanogenerators based on various polymeric materials are highly efficient and robust. Self-powered sensors based on these nanogenerators are highly efficient, sensitive, and cost-effective. Different smart materials based on metal oxides, MXENEs, carbon-based materials are used in nanogenerators for high output power and self-powered sensing properties. Smart materials possess greatly enhanced electromechanical features, including exceedingly high piezoelectric and triboelectric coefficients thereby broadening the scope of their application to sustainable energy. Moreover, these materials possess sufficient structural flexibility and rigidity to enable the seamless incorporation of nanogenerators into wearable electronics, medical devices, and IoT systems. In addition, the capability of smart materials to respond to external forces such as mechanical stress and temperature makes these nanogenerators even more reliable and functional in practical applications.