Pliant and versatile polymeric films engineered for electromagnetic interference (EMI) shielding play a pivotal role in driving the evolution of telecommunications, wearable electronics, and next-generation AI platforms. In this work, poly(p-phenylene benzobisthiazole) (PBO) fibers are subjected to sequential acid treatment with MSA/TFA mixture and subsequent deprotonation to afford well-defined PBO nanofibers (PNF). Water-dispersible silver nanowire (M-AgNWs) is synthesized via a controlled polyol reduction process coupled with Ag–S coordination surface functionalization. Then, M-AgNWs/PNF composite films are fabricated through vacuum-assisted filtration followed by thermal compression. The synthesized M-AgNWs/PNF composite films demonstrate remarkable multifunctional performance at a 50 wt.% M-AgNWs loading, which deliver an electrical conductivity (σ) of 4545 S/cm, superior X-band EMI shielding (81 dB), a thermal conductivity (λ) of 21.7 W/(m·K), and the tensile strength can be flexibly tuned within the range of 101.3 to 181.1 MPa. First-principles density functional theory (DFT) simulation results confirm that HEDS adsorbs onto AgNWs through Ag–S coordination, and the functionalized M-AgNWs can form efficient electrically and thermally conductive networks within PNF, thereby improving the EMI shielding and mechanical properties of the M-AgNWs/PNF composite films. Furthermore, M-AgNWs/PNF composite films demonstrate rapid, reversible photothermal and electrothermal responses. Under simulated sunlight irradiation with a power density of 120 mW/cm², the surface temperature of M-AgNWs/PNF composite films rapidly rise from room temperature to 74.8 °C. Concurrently, under a voltage of 3.5 V, the surface temperature quickly escalates to 79.4 °C. This work offers an effective approach to fabricating lightweight, high-performance EMI shielding composites suitable for aerospace and integrated electronic devices.