Inverse methods have become increasingly prevalent for determining the constitutive parameters of materials from complex experiments involving heterogeneous stress and strain states. The key advantage of employing heterogeneous stress states is the ability to simultaneously test various loading conditions, thereby collecting a more comprehensive dataset to identify advanced material models with reduced experimental effort. In recent years, substantial progress has been made in the field of plasticity, using the virtual fields method (VFM) to identify advanced constitutive models. This paper explores the extension of the VFM approach to encompass temperature effects, introducing a novel testing methodology that generates heterogeneous temperature fields in conjunction with heterogeneous stress and strain fields within the specimen's region of interest. These fields are measured using stereo-DIC and a matrix of thermocouples. The study employed a Gleeble system to heat a specifically designed and optimized specimen made of high-strength steel. Subsequently, the VFM was employed to identify the thermomechanical behavior of the material across a broad temperature range, specifically ranging from 200 to 700 °C. The resulting findings are compared with observations from single tests conducted at different constant temperatures.