We demonstrated a facile fabrication of lithium niobate (LNO) nanostructures embedded in polyvinylidene fluoride (PVDF) using ultrasound irradiation followed by a solvent-casting method and assessed their use towards biomechanical and wave energy harvesting. The physicochemical characterizations of LNO/PVDF nanocomposite films, such as FE-SEM, FT-IR, laser-Raman, and mapping analyses, ensure the formation of uniformly dispersed LNO nanostructures in PVDF matrix with enhanced electroactive β-phase. A piezoelectric nanogenerator (PENG) was constructed using LNO/PVDF nanocomposite with different weight ratios of LNO, and their energy harvesting performances were investigated. The 5 wt.% LNO/PVDF PENG showed better energy harvesting properties, generating a high voltage of 44 V, short-circuit current of ∼0.45 µA, power density (2.2 µW cm−2), and excellent stability. The LNO/PVDF PENG, when placed in the human body, shows an output voltage of 2.6 V, even under minimal deformation applied to the device, suggesting better energy-conversion properties. To evaluate the wave energy harnessing property, the LNO/PVDF PENG was placed under water, which shows the difference in voltage output from 5.43 to 14.7 mV (low to high) with respect to the variation in wave energy. Our experimental findings ensure that LNO/PVDF PENG will act as a suitable power source for next-generation wearable and portable electronics.