This study focuses on characterizing the thermo-viscoplastic behavior of a glass fiber reinforced polypropylene through an advanced characterization technique. Based on a preliminary work addressing a mechanical characterization from conventional uniaxial tests, the proposed rheological model is calibrated using the database of in-plane equi-biaxial tensile tests on a dedicated cruciform specimen geometry from room temperature up to 140°C. The Finite Element Model Update (FEMU) method is employed for parameter calibration. A comparative analysis with the model calibrated from prior uniaxial tests is conducted through finite element simulations of a forming process. This investigation includes a parametric study to objectively assess the impact of the behavior law on forming force and final profile. This parametric study has direct implications for the simulation of an original forming process. The ability to identify the differences in forming outcomes based on different behavior laws enhances the predictive accuracy of the simulations. This ensures that the chosen behavior law aligns closely with the real behavior of the material during forming.