Achieving simultaneous enhancement of electrical conductivity and wear resistance in copper alloys remains challenging because conventional strengthening strategies often introduce additional electron-scattering sources and degrade electrical transport. In this work, a trace Y₂O₃-assisted interface-engineering strategy was developed to regulate the microstructural evolution of spark-plasma-sintered Cu-Ni-Mn-Si alloys. The effects of Y₂O₃ addition on phase constitution, grain-boundary evolution, electrical transport, and tribological behavior were systematically investigated. The results demonstrate that Y₂O₃ does not significantly alter the Cu matrix phase constitution but effectively modifies interfacial evolution during SPS consolidation. Moderate Y₂O₃ addition (0.08 wt.%) produces the most homogeneous grain structure with the smallest average grain size of 4.83 μm through grain-boundary stabilization and particle-pinning effects. However, the optimum functional performance is achieved at a higher Y₂O₃ content of 0.15 wt.%, exhibiting the highest electrical conductivity of 55.37%IACS, the lowest wear loss of 1.24 mg, and the narrowest wear scar width and depth of 861 μm and 23 μm, respectively. The superior conductivity–wear synergy of the 0.15 wt.% Y₂O₃ alloy is associated with the combined effects of microstructural and interfacial regulation, which may influence electron transport and resistance to material removal during sliding. This work reveals that trace additions of rare-earth oxides provide an effective interface-engineering approach to overcoming the conventional conductivity–wear trade-off in powder-metallurgy copper alloys and offer new insights into the design of multifunctional electrical contact materials.