The rapid growth of wearable technology has significantly enhanced the capabilities of wearable sensors, transitioning from simple attachments of rigid electronics to the more comfortable and adaptable integration with soft substrates. Among these, flexible piezoresistive pressure sensors are particularly notable for their straightforward and reliable signal readout. Fiber, yarn, and textile-based sensors, which allow for multiscale material and structural engineering, present ideal solutions for achieving sensors with excellent wearability, sensitivity, and scalability potential. Innovations in materials and the advancement of artificial intelligence (AI) have further enhanced sensor performance, adding multifunctional capabilities and broadening their applications. This review systematically examines fiber, yarn, and textile-based piezoresistive pressure sensors, covering fundamental mechanisms, key performance metrics, conductive and substrate materials, structural designs, fabrication techniques, multifunctional integrations, and advanced applications in healthcare, fitness, and human–machine interaction, augmented by machine learning (ML). Finally, the review discusses sensor design and technical considerations, material–structure–property engineering, scalable production, performance evaluation, and offers recommendations and prospects for future sensor research and development. This comprehensive overview aims to provide a deeper understanding of current innovations and challenges, facilitating the advancement of flexible and intelligent wearable sensing technologies.