This paper presents the results of an experimental study about the durability of E-glass fibre reinforced polymer (GFRP) pultruded profiles when exposed to environmental degradation agents. Small-scale coupons obtained from commercial GFRP profiles, made of either unsaturated polyester or vinylester resins, were exposed to natural ageing in the city centre of Lisbon, an urban Mediterranean environment, during 42 months (3.5 years) and to artificial accelerated ageing in a Q-Lab Ultraviolet accelerated weathering chamber (QUV) chamber up to 3000 h. The effects of such exposure conditions on both types of profiles were assessed and compared regarding the changes on the following physical, chemical, aesthetical, and mechanical properties: (1) colour and gloss variations, (2) viscoelastic response, evaluated by means of dynamic mechanical analysis (DMA), (3) mechanical response in tension, bending and interlaminar shear, and (4) chemical changes, assessed through Fourier transform infrared spectroscopy (FTIR). Both types of environmental exposure caused significant aesthetical changes. Mechanical and viscoelastic properties presented slight changes, suggesting evidence of post-curing phenomena and confirming that ultraviolet (UV) radiation affects essentially the outermost layers of GFRP profiles. In general, the GFRP profile made of polyester presented worse durability performance than the vinylester one, in terms of mechanical performance and especially of aesthetical (surface) performance. QUV and natural ageing could be correlated, particularly in what concerns colour and gloss changes; regarding physical and mechanical changes, in general, properties after ageing in those environments are of the same order of magnitude and exhibit comparable variation trends.