<p>Zn-doped bornite compounds (Cu₅Fe₁₋_xZn_xS₄, <i>x</i> = 0–0.06) were synthesized using mechanical alloying followed by hot pressing, and the effects of Zn substitution on phase stability, structural evolution, charge transport, and thermoelectric performance were investigated. All compositions exhibited a stable single-phase orthorhombic bornite structure without detectable secondary phases, indicating successful incorporation of Zn into the Fe sublattice. Zn substitution induced anisotropic lattice distortion, characterized by a slight contraction along the <i>a</i>-axis and expansions along the <i>b</i>- and <i>c</i>-axes, resulting in a gradual increase in unit cell volume while maintaining a homogeneous solid-solution structure. With increasing Zn content, the hole carrier concentration increased, leading to enhanced electrical conductivity, whereas the Seebeck coefficient gradually decreased, reflecting the trade-off between carrier concentration and thermopower. In contrast, the total thermal conductivity was significantly reduced by Zn substitution compared with undoped Cu₅FeS₄. The minimum total thermal conductivity of 0.32&#xa0;W·m^-1·K^-1 at 523&#xa0;K, with a corresponding lattice thermal conductivity of 0.24&#xa0;W·m^-1·K^-1, was achieved for Cu₅Fe_0.98Zn_0.02S₄, which is attributed to enhanced phonon scattering arising from mass fluctuation and point-defect disorder induced by Zn substitution at the Fe sites. As a consequence of the combined optimization of electrical and thermal transport properties, Cu₅Fe_0.96Zn_0.04S₄ exhibited a maximum power factor of 0.51&#xa0;mW·m^-1·K^-2 at 723&#xa0;K, corresponding to an improvement of approximately 21% relative to undoped Cu₅FeS₄ (0.42&#xa0;mW·m^-1·K^-2), while the highest dimensionless figure of merit, ZT = 0.63 at 723&#xa0;K, was obtained for Cu₅Fe_0.98Zn_0.02S₄, representing an enhancement of about 34% compared with Cu₅FeS₄ (ZT = 0.47).</p>