Oil -based polymeric resins are widely used in the manufacture of fibre -reinforced polymer (FRP) composites, contributing up to 70 % to their total weight. In an effort to reduce the dependence on oil -based feedstock, bio-based alternatives are being increasingly investigated. This study comprises a cradle -to -gate life cycle assessment (LCA) of a bio-based unsaturated polyester resin (UPR) and of glass-FRP (GFRP) composites produced with it using the vacuum infusion method. The bio-based unsaturated polyester prepolymer was developed by partially replacing oilbased chemical components with bio-based alternatives, namely fumaric acid, isosorbide, and 1,3-propanediol. Additionally, the use of the carcinogenic reactive diluent styrene was reduced by partial replacement (50 %) with 2-hydroxyethyl methacrylate. As benchmark, an oil -based UPR obtained from a typical formulation has been considered. The environmental profiles of resins, composites and of the production technique have been analysed to identify their relative contribution to the environmental burdens, which were estimated considering various impact categories. The LCA study revealed lower environmental impact from the bio-based UPR compared to its oil -based counterpart in most categories, namely climate change (total) (CCT, -75 %), ozone depletion (OD, -73 %), photochemical ozone formation (PCOF, -27 %), resource use (fossils) (RUF, -35 %), resource use (minerals and metals) (RUMM, -87 %), non-renewable primary energy (NRPE, -35 %); on the other hand, the conventional UPR was found to perform better in acidification (AC, -54 %), eutrophication (freshwater) (EFW, -55 %), eutrophication (terrestrial) (ET, -76 %), and renewable primary energy (RPE, -92 %) categories. Fumaric acid, isosorbide, and 1,3-propanediol used in the bio-based UPR were identified as the major contributors to impact categories. However, carbon sequestration from the production of 1,3-propanediol and fumaric acid together is responsible for a reduction of 54 % in the CCT indicator relative to considering the impacts from the net carbon emitting monomers alone. Similarly, the bio-UPR based GFRP composite has been found to perform better in CCT (-31 %), OD (-48 %), PCOF (-6 %), RUF (-17 %), RUMM (-10 %), and NRPE (-17 %), while the oil -based counterpart outperformed in AC (-26 %), EFW (-31 %), ET (-46 %), and RPE (-80 %). The single score of EN 15804:2012 + A2:2019 method reveals the better environmental performance of both bio-based UPR and its corresponding GFRP composite comparing to the conventional counterparts. These findings have the potential to support the selection, optimization, and design of more sustainable fibre -polymer composite materials for several industries, namely for structural applications in the construction sector.