The percolation threshold in a composite depends on the processing conditions used to fabricate it along with the size and shape of the filler and the matrix. In this study, borosilicate glass microspheres were used as the matrix material, and nanosized antimony tin oxide (ATO) particles were used as the filler. The glass microsphere/ATO composites were fabricated by hot pressing at temperatures in the range between the glass transition temperature and the softening temperature of the glass to control the viscosity. The pressure and temperature applied allowed the ATO to be confined to the spaces between certain glass particles, forming percolating networks at low volume fractions of the ATO. The viscous flow of the glass allowed for the composite to have near full densities, while allowing for the nanoparticle segregation to occur. Even though apparently similar microstructures were made using different heating schedules, the percolation behavior and electrical conductivity showed noticeable differences. The percolation threshold ranged from 0.1 to 2.5 phr (parts per hundred glass) and the change in electrical conductivity was around seven to nine orders of magnitude. The differences were attributed to the interaction of the segregated ATO particles with one another. The electrical properties were examined using ac impedance spectroscopy along with current atomic force microscopy (C-AFM), which allowed for valuable insights in the structure–property–processing relationships in these materials.