Triboelectric nanogenerators have the ability to harvest low- and mid-frequency vibrational energy from the environment; however, achieving stable performance of the nanogenerator device in high-temperature conditions remains challenging. In this work, a flexible and temperature-stable polyvinyl alcohol (PVA)/layered double hydroxides (LDH) nanocomposite-based triboelectric nanogenerator was developed to harvest unexploited vibrational energy for the first time. Crystalline ZnAl LDH nanosheets grown by a hydrothermal route are used to fabricate the high-performance flexible nanogenerator. The ZnAl LDH exhibits fire-retardancy and high-temperature stability (∼500 °C). A triboelectric nanogenerator based on the ZnAl LDH-PVA nanocomposite generated a very high output voltage of 60 V even under a low vertical pressure of 1 kgf. Surprisingly, the developed device shows ultra-stable output performance even up to a temperature of 200 °C. In addition, a ZnAl LDH-nanosheet-reinforced PVA nanocomposite film shows very high dielectric constant of about 5 × 105 at the low-frequency side. The tremendous increase in the output voltage and stable performance are discussed in terms of the high dielectric constant and synergistic effect of the LDH nanosheets and PVA. Furthermore, the device was also used to monitor human body movements such as finger and wrist bending to develop self-powered sensors.