The use of thermoplastics in the automotive industry is continuously increasing. Design of parts require the characterization and numerical modelling of thermo-mechanical behaviour of those materials under wide strain rate (0–300 s−1) and temperature ranges (−30 °C to +85 °C). Large and costly experimental campaigns are therefore necessary to identify all behaviour's sensitivities. Yet, the time-temperature-superposition (TTS) principle may be a powerful tool to strongly reduce the number of required tests. This paper demonstrates the possibility to extend this principle to the viscoplastic domain while keeping the same shift factors identified for viscoelasticity. So, a limited number of tests (DMA and tensile tests at room temperature only) now enable the characterization of whole thermoplastic behaviour. This new approach is implemented in a viscoelastic, viscoplastic behaviour model. A good correlation between numerical simulations and experiments validate the approach.