With about 2/3 of all utilized energy is being lost as heat. Thermoelectric materials can convert waste heat to electrical energy, and it will have significant role in future energy management. A careful balance between electrical and thermal transport is essential for optimizing the thermoelectric performance. Achieving glass-like ultra-low thermal conductivity in crystalline solids with high electrical conductivity, a crucial requirement for high-performance thermoelectrics, continues to be a grand challenge. Despite this inherent trade-off, the experimental realization of an ideal thermoelectric material with a phonon-glass electron-crystal (PGEC) nature has rarely been achieved. We demonstrated high thermoelectric performance with a near room-temperature figure of merit, zT ~1.5 and a maximum zT ~2.6 at 573 K by optimizing atomic disorder in Cd doped polycrystalline AgSbTe2. 1, 2 Cadmium doping in AgSbTe2 enhances cationic ordering, which simultaneously improves electronic properties by tuning disorderinduced localization of electronic states and reduces lattice thermal conductivity via spontaneous formation of nanoscale (~2-4 nm) superstructures. Recently, we showed that isovalent Yb-doping induced enhanced atomic ordering decreases the overlap between the hole and phonon mean free paths and consequently leads to a PGEClike transport in AgSbTe2. 3 A twofold increase in electrical mobility is observed while keeping the position of the Fermi level nearly unchanged and corroborates the enhanced crystalline nature of the AgSbTe2 lattice upon Yb doping for electrical transport, which leads to zT ~2.4 at 573 K. These achievements highlight the potential of our approach in enhancing the thermoelectric performance of the material by tuning its inherent atomic disorder which can be applicable to other thermoelectric materials.4