Present study aims to develop a 3D thermo-mechanical numerical model to better understand the influence of elevated temperature on the bond between the GFRP bars and concrete in RC structural elements. The relevant constitutive thermal and mechanical parameters of the bond were calibrated using experimental measurements, including pull-out tests under different elevated temperatures. The accuracy of the numerical thermo-mechanical predictions was first confirmed by pull-out test simulation, then the modelling strategy was transferred to RC thin slabs. Good accordance of experimental and numerically predicted temperature fields was followed by the verification of the complete methodology through comparison of experimental and numerical thermo-mechanical slabs’ response. The relevant laboratory experimental measurements and observations confirmed the accuracy of the developed numerical modelling, emphasizing the importance of proper selection of material parameters and their temperature dependencies. This work contributes to the improvement of simulation strategies for GFRP RC structures in elevated temperature environments and tends to increase the confidence in adopting GFRP reinforcement bars in concrete design.