The influence of ball milling followed by Spark Plasma Sintering (SPS) on the thermoelectric properties of the Cu15As30Te55 glass composition has been investigated by means of X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. The microstructure, composition, and thermal stability of the ball-milled samples before and after SPS have been correlated with the electrical and thermal transport properties. Upon ball milling, a glass-to-glass transformation is evidenced for short ball-milling times, followed by crystallization of the metastable beta-As2Te3 phase within the glassy matrix. This glass-to-glass transformation favors the occurrence of the beta-As2Te3 phase during the SPS process. A maximum figure of merit ZT of 0.29 at 400 K is obtained in the sample exhibiting the largest beta-As2Te3 crystalline fraction. This ZT value is twice as high as the value obtained for the glass-ceramic sintered from non-ball-milled powder.