Abstract: This article presents results of experimental investigations of the durability of glass-fibre-reinforced polymer (GFRP) pultruded profiles exposed to typical environments of civil engineering applications. Specimens obtained from commercial GFRP profiles made of unsaturated polyester and vinylester resins were subjected to immersion in (i) demineralised water and (ii) salt water at 20 °C, 40 °C and 60 °C for up to 18 months, (iii) continuous condensation at 40 °C for up to 9 months and (iv) accelerated ageing in a QUV chamber for up to 3000 h. The effects of such exposure conditions on both types of profiles were analysed in what concerns their (i) mass changes, (ii) viscoelastic response, evaluated by means of dynamic mechanical analysis (DMA), (iii) mechanical response in tension, bending and interlaminar shear, and (iv) chemical changes, assessed through Fourier transformed infrared spectroscopy (FTIR). Hygrothermal ageing had significant influence on the material performance, namely on the mechanical response – demineralised water immersion caused a higher level of degradation, compared with salt water immersion, and results show a clear competition between moisture-induced plasticisation and residual post-curing of the composite matrix. Following QUV exposure, although considerable aesthetical changes were observed, the viscoelastic response and mechanical performance of both profiles were not remarkably affected, confirming that UV radiation affects essentially the outermost layers of GFRP profiles. In general, the GFRP profile made of vinylester resin exhibited better durability performance, when compared with its polyester counterpart.