Next-generation biomedical devices increasingly require integrated energy harvesting and miniaturized electronic components to achieve self-sustaining operation without external power sources. However, most currently available systems remain rigid and bulky, impeding effective mechanical and biological interfacing with soft tissues. Hydrogels, with their high water content, tunable elasticity, and excellent biocompatibility, have emerged as ideal candidates for developing conformal and tissue-compliant electronics. To overcome the limitations of battery-powered implants, recent studies have focused on harvesting biomechanical energy - particularly via piezoelectric nanogenerators (PENGs) - as a sustainable alternative. The integration of PENGs into hydrogel matrices has led to the emergence of piezoelectric hydrogels (PHs), a novel class of soft, biocompatible, and self-powered biomaterials. These hybrid materials combine the mechanical adaptability of hydrogels with the energy conversion capabilities of piezoelectric materials, enabling new paradigms in implantable and wearable electronics. This review presents a comprehensive overview of PHs, including piezoelectric material classifications (ceramics, polymers, nanocomposites), fabrication strategies of natural and synthetic PHs, and their device-level performance under physiological conditions. Furthermore, we discuss the application of PHs in skin wound healing, peripheral nerve regeneration, and the repair of bone and cartilage tissues. Finally, we provide a future outlook emphasizing the need for mechanistic insights, improved output performance, and standardized in vivo evaluations to accelerate the clinical translation of PH-based self-powered bioelectronics.