The mixed-ion electron conductor, Ag₂Se, has shown strong potential as a thermoelectric material operating near room temperature. In this study, we demonstrate that the incorporation of polyaniline (PANI) into Ag₂Se forms Ag₂Se/PANI nanocomposites with significantly enhanced thermoelectric performances. Ag₂Se was synthesized using a hydrothermal method followed by hot pressing to obtain dense composite pellets. The novelty of this work lies in the systematic tuning of the PANI content and its dual role in enhancing electrical transport while suppressing lattice thermal conductivity. Microstructural analysis reveals that PANI-induced defects, such as dislocations and point defects, effectively scatter phonons at multiple scales, resulting in a remarkably low lattice thermal conductivity (κₗ ≈ 0.08 Wm⁻1 K⁻1) at 393 K. Simultaneously, PANI improves carrier mobility by modifying the Coulomb potential at grain boundaries, reducing interfacial energy barriers. These effects lead to an improved power factor of 2028 μWm⁻1 K⁻2 and a peak figure of merit (zT ≈ 0.67) at 393 K for the 0.5 wt% PANI sample. This study introduces a novel polymer-assisted interface engineering approach to improve the thermoelectric performance of Ag₂Se-based materials.