<p>This study describes an environmental life cycle assessment (LCA), including an ecotoxicity analysis, of municipal solid waste incinerator bottom ash produced by a Portuguese waste-to-energy power plant. The LCA followed a “cradle-to-gate” (A1-A3) approach of the bottom ash production process itself and compares concrete mixes containing it with those using fly ash or Portland cement. The study uses site-specific data as input in the SimaPro software to evaluate the impacts associated with producing 1 tonne of bulk bottom ash at the plant’s exit gate. The results infer positive outcomes in all categories except natural resources depletion and renewable energy consumption: global warming potential decreased by 20% (–0.18 kg CO₂eq) and non-renewable energy demand also improved with a 1 724 MJ reduction. These were attributed to waste treatment, especially recycling steel, aluminium, and ferrous and non-ferrous metals following sorting, which is a prerequisite for bottom ash processing. Applying these results to alkali-activated concrete mixes highlighted a 59% reduction in acidification potential and a 57% reduction in non-renewable energy use, despite a 442% increase in global warming potential compared with mixes using alternative binding agents. In the second part of the study, detailed chemical and biological analyses compared binders in bound and unbound forms. Ecotoxicity-related trials showed a shift from Class IV to Class III, with toxicity units for <i>Daphnia magna</i> decreasing by 89% when substituting cement with alkali-activated bottom ash, thereby demonstrating the material’s technical viability from an environmental hazard perspective.</p>