The growing demand for clean and sustainable energy sources, triboelectric nanogenerators (TENGs) have emerged as an efficient solution for harvesting electrical energy from biomechanical motion. In this study, we report the fabrication of TENG using sonochemically prepared graphene/polydimethylsiloxane (SGP) nanocomposite films as an active tribo-negative layer and polyethylene oxide (PEO) as a tribo-positive layer. The nanocomposite film with 0.75 wt% graphene exhibited superior triboelectric performance, achieving a high output voltage of 415 V and a current of 5.06 µA, respectively. The surface potential characteristics and charge transfer behaviour were systematically studied using Kelvin probe force microscopy (KPFM) and density functional theory (DFT) simulations, suggesting enhanced charge-trapping capability in the nanocomposite film is due to the presence of graphene in the polymer matrix. The fabricated SGP-TENG was successfully integrated into practical applicability such as human motion monitoring, gaming interfaces, and power-point control confirming its potential in futuristic self-powered systems.