This paper presents experimental and numerical analyses of the thermomechanical behaviour that takes place in SAE1020 mild steel cylindrical specimens during the conventional tensile test. A set of experiments has been carried out in order to obtain the stress-strain curve and the diameter evolution at the neck which allow, in turn, to derive the elastic and hardening parameters characterizing the material response. Temperature evolutions have also been measured for a high strain rate situation. Moreover, a finite element large strain thermoelastoplasticity-based formulation is proposed and used to simulate the deformation process during the whole test. Some important aspects of this formulation are discussed. Finally, the results provided by the simulation are experimentally validated.