Natural rocks of magmatic origin are alternative precursors in alkali-activated materials and provide opportunities in the search for more environmentally friendly binders compared to portland cement. The pumice is one of these rocks and its amorphous structure and chemical composition make it one of the candidates as a precursor in producing geopolymer binder when finely ground. Since the majority of the pumice reserves are located in Turkey increases its potential utilization in this area, even more. This paper evaluates the physical, mechanical, and microstructural properties of geopolymer pastes and mortars manufactured with pumice powder (PP) and ground granulated blast furnace slag (BFS) with the activating agents sodium hydroxide (NaOH), potassium hydroxide (KOH), and sodium silicate (SS) solution. The experimental results showed that the compressive strength of the geopolymer pastes was mainly affected by the activator concentration and the PP ratio, rather than the activator type, for single activator mixes. However, the incorporation of SS changed this trend as the KOH and SS combination resulted in higher compressive strength compared to the NaOH and SS. The gradual increase of the PP ratio in the mix design decreased the density and thermal conductivity, on the other hand, increased the water absorption values of the geopolymer mortars. However, the physical properties were insignificantly changed in geopolymer mortars incorporating 60, 70, and 80% of PP in the binder.