This study aimed to evaluate the effectiveness of sodium hydroxide and ground granulated blast-furnace slag (GGBFS) in stabilizing iron ore tailings. The distinctive contribution of this study lies in the integrated assessment of elemental leaching, changes in the chemical environment, microstructural evolution during stabilization, and life-cycle impacts. Sodium hydroxide concentrations ranging from 0 to 5 M were first investigated, followed by the addition of 0–9 wt.% GGBFS at a fixed NaOH concentration of 3 M. The pH, electrical conductivity, microstructure, apparent surface porosity, and leaching behavior of Ni, Cu, Zn, Pb, and Ba were evaluated. The results showed that GGBFS addition was more effective than increasing the alkaline activator concentration alone in reducing elemental mobility. The mixture containing 3 M NaOH and 9 wt.% GGBFS exhibited the lowest leaching concentrations of Ni, Cu, Zn, Pb, and Ba, at 0.10, 0.12, 0.12, 0.018, and 0.40 mg/L, respectively. The apparent surface porosity of this mixture was also reduced to 0.81%. The life-cycle assessment showed that the scenario containing 9 wt.% GGBFS and 5 M NaOH reduced global warming potential, abiotic resource depletion, particulate matter formation, and land use by approximately 32%, 33%, 22%, and 16%, respectively, compared with stabilization using 9 wt.% Portland cement, although the human toxicity potential increased by approximately 8%. Overall, the proposed system showed considerable potential for reducing elemental mobility, while selection of the final mixture requires a balance between stabilization performance and life-cycle impacts.