With rapid development of wearable electronic technology, flexible thermoelectrics have become an important research topic in the field of wearable energy devices, owing to their sustainable power-supply ability, flexibility, and portability. However, the application of flexible thermoelectric devices in wearables is limited by their low stretchability, lack of breathability, and poor functional integration. Fiber-based stretchable thermoelectric devices with one-dimensional structure feature properties such as small size, lightweight, large deformation, and weavability, which make them suitable for integration into wearable fabrics. In addition, these devices can harvest thermal energy from human body. In this study, the materials, structures, and processing techniques developed for the fabrication of stretchable fiber thermoelectric devices are reviewed. Thereafter, their applications in self-powered sensing, energy harvesting, and thermoelectric cooling are discussed. Finally, a summary and an outlook are provided on the development of fiber thermoelectric devices wherein the key challenges of their practical applications are highlighted.