The increasing focus on sustainable agricultural practices and the circular bioeconomy has driven interest in the valorization of agro-industrial residues. Olive leaves (OLs), a by-product of pruning operations, represent a rich source of bioactive compounds such as polyphenols, as well as structural materials like cellulose. This study aims to assess the environmental sustainability of a novel biorefinery process developed to extract polyphenols and cellulose from Olea europaea L. cv. Caiazzana leaves using a Life Cycle Assessment (LCA) approach. The LCA was conducted in accordance with international standards, adopting a cradle-to-gate system boundary. The functional unit was defined as 1 kg of OLs processed. Primary data were collected from laboratory-scale experiments, while secondary data were sourced from the Ecoinvent database. The process flow included mechanical pre-treatment, polyphenol extraction, separation and purification steps, and cellulose recovery from the residual biomass. The environmental impacts were assessed using the ReCiPe 2016 Midpoint and Endpoint method. The LCA revealed that the main environmental hotspots were energy consumption during the drying and extraction phases and the use of chemical reagents. The most affected impact categories included climate change, freshwater eutrophication, and human toxicity. However, the co-extraction of high-value polyphenols and cellulose significantly improved the process's eco-efficiency. A sensitivity analysis indicated that replacing fossil-based electricity with renewable sources could reduce the total GHG emissions by over 40%. The valorization of OL pruning residues into bioactive compounds and cellulose presents a promising strategy to reduce agro-industrial waste and promote resource efficiency. Integrating LCA in early-stage process development highlights potential environmental trade-offs and improvement opportunities, supporting the transition toward sustainable and circular agricultural systems.