Abstract <p>This work proposes a mathematical model for describing the nonlinear deformation of isotropic materials under non-isothermal loading. The model is formulated within a thermodynamic framework employing internal state variables, whose number, physical nature, and kinetic equations are explicitly defined. The proposed formulation yields a constitutive relation and the heat conduction equation, which together form the system of governing equations for the coupled thermoplastic boundary-value problem. As a special case, the model reduces to the constitutive framework of endochronic thermoplasticity. Analysis of the constitutive relations yields functional dependencies for the model’s material parameters. The model’s practical applicability is validated by comparing its numerical predictions with experimental data for aluminum alloy 7075-T6. The favorable agreement confirms the model’s effectiveness and its utility for analyzing the thermomechanical behavior of isotropic materials.</p>