The Martian atmosphere, with its high CO2 concentration (>96%), low pressure (~1 kPa), and low temperatures (~−100 °C), offers favourable conditions for oxygen production via plasma-catalytic CO2 dissociation, representing a key in-situ resource utilisation strategy for future missions. The packed-bed dielectric barrier discharge reactor is widely used for low-temperature plasma catalysis. While extensively studied under terrestrial conditions, the discharge behaviour under Martian pressure transitions from filamentary streamers to a uniform glow discharge, fundamentally altering catalyst surface processes and chemical pathways. The study shows that at atmospheric pressure the discharge is filamentary, whereas at Mars-like low pressure (1 kPa) it becomes a uniform glow due to greater electron mean free path and particle mobility. Although dielectric bead polarization enhances the electric field and lowers breakdown voltage at all pressures, its effect on discharge distribution differs: at high pressure, discharge intensifies directly above beads as stable streamers, while at low Martian pressure it strengthens laterally around the beads. A larger gap lets the bead surface act as an effective cathode, forming a visible cathode fall glow, whereas a smaller gap brightens the surrounding glow and shrinks the dark region. Discharge weakens notably between closely packed beads, indicating that the packed-bed structure must be redesigned for efficient PB-DBD operation at 1 kPa.