<p>SnSe represents a promising thermoelectric material for medium-temperature applications owing to its ultralow lattice thermal conductivity. However, the poor electrical conductivity of n-type polycrystalline SnSe significantly hinders its practical application. Herein, we propose a dual-functional strategy employing InBr₃ doping to synergistically enhance electrical transport while suppressing lattice thermal conductivity. For the first time, we demonstrate the successful construction of a Br-enriched conductive network within the SnSe matrix. The incorporation of In³⁺ and Br⁻ introduces high-density charge carriers, while Br forms percolative conductive networks, resulting in a remarkable enhancement of carrier mobility to ∼20.64 cm² V⁻¹ s⁻¹. Simultaneously, the lattice thermal conductivity is substantially reduced to ∼0.25 W m⁻¹ K⁻¹ through the formation of multi-scale defects, including dislocations and Br-rich nanowires, which effectively enhance phonon scattering. As a result, we achieve a peak figure of merit of <i>ZT</i> ∼1.41 at 823 K, with an average figure of merit of ∼0.42 over the temperature range of 323–823 K. This work provides a universal paradigm for decoupling electron-phonon interactions in thermoelectric materials, offering new insights for the optimization of thermoelectric performance.</p>