A synopsis of an experimental program on the development of a sustainable fly ash–slag blended geopolymer mortar (GPM) and lightweight geopolymer concrete (LGPC) is presented. Geopolymer mortar mixes were prepared incorporating industrial by-products and sustainable desert dune sand to study the effect of different mixing variables, including binding materials, curing temperature, and alkaline activator solution composition and content, on the rheological and mechanical performance. Optimum mix designs were then formulated into producing LGPC samples with different binding materials and curing temperature. Lightweight geopolymer concrete specimens exhibited a brittle behavior with a weakened structure due to low-strength lightweight aggregates. Lightweight geopolymer concrete made with dune sand and a fly ash to slag ratio of $3:1$ resulted in the highest compressive strength when cured for 24 h at 60°C. Microstructure characterization of LGPC specimens was also conducted. Scanning electron microscopy and differential scanning calorimetry showed the coexistence of an aluminosilicate hydrate geopolymer gel and aluminum-modified $\mathrm{C}─\mathrm{S}─\mathrm{H}$ gel as the main polymerization reaction products in an amorphous geopolymeric microstructure.