AgSTe based materials have recently been identified as promising thermoelectric materials that have favorable properties at room temperature. They are usually obtained by conventional processes involving melting, annealing, and sintering, which incur significant energy and time expenditures. The present investigation involved the synthesis of Ag20S7Te3 compounds by a fast non-equilibrium methodology, i.e., plasma activated sintering from raw elemental powders. The monoclinic Ag20S7Te3 phase crystal was successfully formed at a temperature of 673 K, accompanied by the presence of a secondary monoclinic phase, Ag2S. The Ag20S7Te3 phase predominated in the monoclinic form, constituting a significant percentage at temperature of 873 K. Furthermore, the thermoelectric figure of merit (zT) of the AgSTe phase at 873 K was determined to be 0.42. The rapid sample synthesis described herein has the potential to significantly reduce the duration required for material synthesis, hence presenting a conspicuous advantage in the context of manufacturing on a wide scale.