Lignocellulosic biomass has received recent attention in Portugal as a key renewable energy source to play an important role in electricity production and advanced technologies are being considered as a promising high efficiency pathway. However, the actual benefits of biomass-to-electricity systems have not been previously assessed in a life cycle perspective. This paper presents the development and implementation of a comparative life cycle model aiming at assessing the full cradle-to-grave energy and environmental performance of alternative lignocellulosic biomass-to-electricity production pathways for Portugal. Twenty-four alternative scenarios have been defined considering different combinations of: i) forest biomass types (residues and energy crops), ii) biomass collection and transportation processes and iii) electricity production technologies (gasification and direct combustion). An extensive data collection has been carried out in Portugal to build the life cycle (LC) inventory for the 24 scenarios. A LC model has been developed based on a systemic description of the various scenarios with the aim of evaluating and finding the most sustainable solutions throughout the various LC stages. The primary energy fossil requirement and the Greenhouse Gas (GHG) emissions associated with the production of 1 MJ of electricity are presented, for each phase of the life cycle. The results calculated for the 24 scenarios show that the fossil energy requirement can vary from 0,062 MJ to 0,166 MJ per MJ of electricity produced. The most efficient pathway is obtained with gasification of forest residues. The processes that require more fossil energy are biomass chipping and transportation (from 19% to 50% of total fossil energy requirements). GHG emissions range from 5,7 gCO₂eq to 11,5 gCO₂eq per MJ of electricity produced. The present analysis demonstrates that biomass-to electricity can be a sustainable option regarding fossil energy use (primary energy savings: 2,1–2,8 MJ/MJ electrical) and GHG emissions avoided (121–228 gCO₂eq/MJ electrical), but advanced energy conversion technologies, namely gasification, must be employed.