Thermoelectric devices represent an emerging technique that holds great promise for improving energy utilization efficiency and the recovery of waste heat energy. In comparison to inorganic or metallic thermoelectric materials, conducting polymers, consisting of a carbon-based π-conjugated backbone, simultaneously possess electrical conductivity of metals and excellent mechanical properties of common plastics. To date, conducting polymers have found great potential/practical applications in various fields. As a well-known conducting polymer, poly(3-hexylthiophene) (P3HT), possessing unique physicochemical properties, is a model system to study electronic/thermal correlations and develop high-performance thermoelectric devices. In this review, state-of-the-art research progresses of P3HT-based materials in thermoelectrics are provided. First, a brief introduction to the thermoelectric effects and advantages of conducting polymers as thermoelectric modules is provided. Then, applications of both pristine P3HT and P3HT-based composites in thermoelectrics are highlighted by citing numerous representative examples. Strategies to improve the performance of P3HT-based thermoelectrics are systematically summarized. An in-depth study of P3HT was conducted, focusing on various aspects such as molecular weight, orientation, morphology/size and structural modification, since many TE factors are related to these parameters, for instance, charge mobility and electrical conductivity. Furthermore, chemical doping also demonstrates great potential in adjusting the thermoelectric performance of P3HT. Additionally, some composites containing P3HT for advanced thermoelectrics are also discussed. Then, we discuss the application and development prospects of P3Ht-based thermoelectric materials in human wearable flexible devices. Finally, the main challenges and prospects of P3HT-based materials and their applications in thermoelectrics are discussed. Hopefully, this review can inspire the development of P3HT-based thermoelectrics.