The use of FRP (Fibre Reinforced Polymer) materials in strategic locations has been shown to successfully strengthen and stiffen structural timber products when required, not only in new structures but also in the upgrading and repair of existing structures (Kliger et al., Eur. J. Wood Wood Prod 74:319–330, 2016; Schober et al., Constr Build Mater 97:106–118, 2015). The addition of such materials which typically have superior properties to that of timber has been shown to significantly improve the flexural performance of timber (Franke et al., Constr Build Mater 97:2–13, 2015; Harte and Dietsch, Reinforcement of timber structures: A state-of-the-art report, Shaker Verlag GmbH, Germany, 2015; Kliger et al., Eur J Wood Wood Prod 74:319–330, 2016; O’Neill et al., Constr Build Mater 145:226–235, 2017; Raftery and Harte, Compos Part B Eng 52:40–50, 2013; Schober et al., Constr Build Mater 97:106–118, 2015; Thorhallsson et al., Compos B Eng 115:300–307, 2017)) however, the long-term performance or the creep behaviour of reinforced structural elements has received less attention in the literature and requires further investigation, particularly as recent innovations in the timber construction industry have resulted in the increased use of mass-timber elements and a greater number of tall timber buildings (Abrahamsen, Mjøstårnet—Construction of an 81 m tall timber building. Internationales Holzbau-Forum IHF, 2017; Harley et al., Proceedings of the World Conference on Timber Engineering (WCTE 2016), 2016; Jockwer et al., Eng Struct 234:111855, 2021; Ramage et al., J Architect 22:104–122, 2017). The long-term behaviour of timber is often complex, particularly when subjected to a variable climate condition and in this study, the creep deflection behaviour of unreinforced and Basalt Fibre Reinforced Polymer reinforced beams are subjected to creep testing at a common maximum compressive stress of 8 MPa in both constant and variable climate conditions. This study builds upon the work produced by the authors (O’Ceallaigh, An Investigation of the Viscoelastic and Mechano-sorptive Creep Behaviour of Reinforced Timber Elements. National University of Ireland, Galway, 2016; O’Ceallaigh et al., Constr Build Mater 259:119899, 2020, 2019, 2018) whereby the creep behaviour of unreinforced and reinforced glued laminated beams over a 75-week period in a controlled constant and variable climate was presented. This study herein presents a significant extension of the experimental creep data from 75 weeks up to a period of 450 weeks or 8.5 years. Over this period, the results have shown that reinforcing timber with an FRP material of superior properties has a positive effect on the creep behaviour of timber elements. In the constant climate, the percentage difference between the unreinforced (Group UC) and reinforced (Group RC) is statistically significant after approximately 103 weeks demonstrating a positive effect of FRP reinforcement on the creep deflection behaviour of reinforced beams. In a variable climate, the mean relative creep results demonstrated a statistically significant difference between the unreinforced (Group UV) and reinforced (Group RV) after just the first relative humidity cycle. This trend has continued for the duration of the creep testing (450 weeks) and further demonstrates that the FRP reinforcement has a statistically significant impact on the creep deflection of structural timber elements. Furthermore, the tested elements were unloaded, and the creep recovery data was also presented. A significant reduction in total creep deflection due to the FRP reinforcement was observed in the results obtained in both a variable and constant climate and once unloaded, the results indicate that a significant proportion of creep can be recovered in beams subjected to a constant climate, however, when subject to a variable climate, there appears to be a significant proportion of non-recoverable deformation. In conclusion, the use of FRP reinforcement can reduce the creep behaviour of structural timber elements but the influence of the climatic conditions is significant, and the magnitude of the creep behaviour is a product of the coupled load and environmental history of the beams.