<p>The transition toward climate-neutral energy systems requires robust comparisons of alternative electricity generation pathways based on consistent life-cycle frameworks. This study performs a cradle-to-gate life cycle assessment of nine electricity production routes under Portuguese conditions, including seven renewable energy-based systems and two fossil-based systems. The renewable pathways comprise direct biomass combustion, upgraded biogas combustion, synthetic biomethane produced via carbon dioxide methanation with green hydrogen, and hydrogen-based electricity generated either from biomethane steam reforming or solar photovoltaic-powered water electrolysis. Hydrogen utilisation was evaluated through both combustion and proton exchange membrane fuel cells. Environmental impacts were quantified across six categories, including global warming potential, acidification, particulate matter formation, human toxicity, land use and water consumption. Results show that fossil pathways remain the dominant sources of greenhouse gas emissions, with coal and natural gas producing approximately 1.28 and 0.79 kg CO₂ eq per kWh, respectively. In contrast, direct biomass combustion exhibits near-carbon–neutral performance (≈ 0.004 kg CO₂ eq/kWh), while electrolysis-based hydrogen pathways achieve zero operational emissions within the assessed cradle-to-gate boundaries (which exclude infrastructure manufacturing). Meanwhile, pathways relying on biogas and biomethane exhibit intermediate climate impacts driven by fugitive methane slip. Overall, the integration of renewable hydrogen and sustainably sourced biomass emerges as a promising strategy for deep decarbonisation of electricity systems. These findings provide quantitative insights to support the transition toward a carbon–neutral Portuguese energy system by 2050.</p>