Although the adoption of self-powered energy harvesting technologies is rapidly increasing, the fabrication of flexible, easy-to-assemble, highly sensitive, and energy-efficient devices continues to pose a significant challenge. Electrospun nanofibrous film-based triboelectric nanogenerators (TENGs) show great promise for mechanical energy harvesting and self-powered sensor applications due to their flexibility, wearability, lightweight, and high electrical output. Herein, a polydopamine (PDA)-treated silver (Ag) nanoparticles (NPs)-decorated titanium dioxide (PDA-Ag/TiO2 NPs) is innovatively incorporated into an electrospun Nylon 66 polymer to construct PDA-Ag/TiO2 nylon composite nanofibrous film (NCNF)-based TENGs (PAT@NCNF TENGs). The prepared nanofibrous films display high dielectric and conductive properties, improving the output electrical performance of the TENG. The electrical output performance of the PAT@NCNF TENG is systematically studied by varying the filler material embedded in the Nylon 66 polymer. The assembled PAT@NCNF TENG exhibits an electrical output of ≈370 V, ≈15 µA, and ≈5.4 W m−2 with an excellent pressure sensitivity of ≈7.88 V kPa−1. The proposed PAT@NCNF TENG is used to harvest various forms of biomechanical energy and to power electronic gadgets. Finally, PAT@NCNF TENG is effectively employed for multifunctional sensing systems to monitor biomechanical actions, detect the pressure and impact of objects, and facilitate Morse code transmission and human gait monitoring applications.