Thermoelectrics are a class of materials that provide interconversion between heat and electricity, with desirable traits such as low thermal conductivity and low electrical resistivity. AgSbTe2 has emerged as one of the leading materials in recent years due to its ultra-low thermal conductivity. However, one major hindrance in undoped AgSbTe2 is its high electrical resistivity and low Seebeck coefficient due to the presence of Ag2Te nanoprecipitates. In this work, we leverage on the combination of an off-stoichiometric composition and a non-equilibrium process to simultaneously enhance the properties of AgSbTe2 and its thermoelectric device performance. Microscopically, the Ag2Te-deficient starting composition combined with a non-equilibrium thermal process suppresses the Ag2Te nanoprecipitates in the material. In addition, it is evident from the density functional theory (DFT) electronic structure that Ag2Te deficiency results in a smaller lattice and higher density-of-states near the Fermi level, which simultaneously lower the electrical resistivity and increase the Seebeck coefficient. As a result, zT as high as 1.7 was achieved at 573 K. Additionally, when combined with a high room temperature zT of 0.75, a power conversion efficiency of 7.3% was achieved at a ΔT of 290 K. Crucially, the strategy in this work can inspire application in other ABX2 material systems to achieve improved thermoelectric performances.