The study reported herein investigates the performance of fly-ash-based geopolymer concretes (FA-GPC) when subjected to various durability tests. The durability of FA-GPC was examined for alkali silica reaction (ASR), chloride induced corrosion, carbonation, and sulfate attack. The ASR in FA-GPC was analyzed for three types of reactive aggregates (siliceous limestone, sandstone, and quartz). The effect of the ASR on FA-GPC was found to depend on the calcium contents of the fly ash (FA). FA-GPC made using Class F FA were found to be less vulnerable to ASR as compared with specimens made using Class C FA. Measured values of expansion were below the 0.1% limit specified by ASTM C1260 [2007, “Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method),” Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA] for all FA-GPC specimens. FA-GPC specimens made from Class F FA exhibited lower corrosion rates and porosity compared to their Class C FA-GPC and OPC counterparts. Overall, FA-GPC specimens showed limited signs of leaching or corrosion product formation, while OPC specimens exhibited the formation of multiple corrosion products along with significant leaching. Carbonation studies on FA-GPCs prepared with Class C and F FA suggested that carbonation had limited effect on geopolymer binders as rates were well below the threshold for initiation of corrosion. In addition, durability tests were performed on the effect of external sulfate attack on geopolymer concrete using calcium, sodium, and magnesium sulfates. The sulfate ingress treatment was accelerated using applied electro kinetics by applying a constant current density of 1 A/m² for 1 week. A decrease in compressive strength was observed due to sodium and magnesium sulfates, while an increase was observed in the case of the calcium sulfates. Geopolymer concrete mortars and pastes perform satisfactorily when exposed to the three sulfate sources, but did not outmatch the performance of OPC Type V cements.