Ternary sulfide AgBi3S5 compound is expected to be a promising thermoelectric material because of its merits such as low electrical resistivity and environmentally compatible composition. In this study, a combined process of mechanical alloying and spark plasma sintering was applied to the fabrication of AgBi3S5 bulk materials, and nearly single phase was obtained by optimizing the sintering conditions, although the mill-derived powders consisted of AgBiS2 and Bi2S3 phases. The electrical conductivity of the AgBi3S5 bulk material decreases from 178 to 79 Scm−1 with raising temperature from 323 to 573 K, while the Seebeck coefficient ranges from −83 to −167 μV K−1, thereby a maximum power factor 221 μW m−1 K−2 achieved at 573 K. It is notable that AgBi3S5 has a low thermal conductivity, ranging from 0.70 to 0.64 W m−1 K−1 from room temperature to 573 K, which is the lowest value reported so far for this material. A peak thermoelectric figure of merit value of 0.20 was obtained at 573 K in the present pristine AgBi3S5 sample.