This paper reports the durability properties of slag-glass powder (GP) geopolymer mortars at different GP contents and compares them with Portland cement mortars (PCM). The slag-GP mixes are activated with 6 M NaOH solution at 0.35 liquid-to-solid ratio. The performance of 28-day cured specimens under high-temperature exposures, wetting-drying and freezing-thawing cycles, water slaking, surface abrasion, and alkali-silica reactions (ASR) are examined. Scanning electron microscopic analysis is carried out to identify the microstructural changes in the material. The study outcomes indicate that an appropriate GP content (10%) enhances the performance of slag-GP binary geopolymers and improves its durability. However, ASR expansion is found to be increased marginally. The geopolymer specimens achieved higher strength and durability than PCM due to a dense and compact microstructure with significant gel formations.