Glasses in the pseudo-binary system (HgS)(x) (GeS2)(1-x) were synthesized over the concentration range of 0.0 <= x <= 0.5. The fundamental glass properties (macroscopic, electric, and vibrational) were studied using differential scanning calorimetry (DSC), direct current (dc) electrical measurements, Raman spectroscopy supported by DFT modeling, and X-ray diffraction. Mercury species in thiogermanate glasses essentially form chain-like (HgS2/2) fragments substituting bridging sulfur between corner- and edge-sharing GeS4/2 tetrahedra. This structural evolution results in a significant monotonic decrease of the glass transition temperatures from 480 to 270 degrees C. The room-temperature dc conductivity changes non-monotonically with increasing HgS content x over a limited range of 4 X 10(-15) to 7 x 10(-13) S cm(-1). The electronic transport in insulating HgS-GeS2 glasses occurs via extended electronic states. Tetrahedral HgS4/4 fragments also appear in the glass network with increasing x. Their exact population needs further advanced structural studies using diffraction techniques.