Geopolymers are eco-friendly materials emerging recently in the construction industry. These alternative binders are formed from by-products rich in silica and alumina, such as fly ash, slag, or metakaolin, mixed with an activating solution known as the alkaline solution. For this research, fly ash from coal combustion was used with an activating solution composed of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) to produce geopolymer mortar. However, the gradual closure of coal-fired power plants will limit the availability of associated fly ash (FA). Therefore, it is necessary to identify alternative materials that can be used as a source of silica and alumina in geopolymers. In this study, FA was thus partially replaced by glass powder (GP), which also exhibits pozzolanic properties, in order to test its effect on the mechanical properties of GPM. Samples with different percentages of GP (0%, 5%, 10%, and 20% by weight) were tested to determine their impact on the compressive strength of GPM. The effect of the molarity of the alkaline NaOH solution on the compressive strength of GPM was also studied; two molarities were tested (10M and 14M) for this purpose. The results showed that the substitution of 5% of FA by GP in GPM with 14M as the concentration of NaOH gives a compressive strength of 48.3 MPa, very close to that of the GPM without GP which gives 47.7 MPa at 90 days. Similarly, 10% substitution of FA with GP also has no major effect on the compressive strength. On the other hand, a higher molarity of NaOH solution showed a higher compressive strength.