The need to understand the thermal response of soils arises in a wide range of geoenergy engineering applications, including deep geological disposal of nuclear waste, geothermal structures, oil and gas drilling, and thermal ground improvement techniques. Although numerous studies have investigated the influence of temperature on soil behavior, the response of unsaturated soils to thermal changes remains highly complex due to the strong coupling among thermal, hydraulic, and mechanical processes. Therefore, a more comprehensive understanding of these coupled mechanisms is required. In this study, a thermo-hydro-mechanical constitutive model is developed to predict the behavior of unsaturated clay soils under varying temperature conditions. The proposed model is based on the constitutive framework developed by the first author and is extended to incorporate temperature-dependent effects. The model is capable of capturing the coupled influence of temperature on both the stress–strain response and hydraulic behavior of unsaturated soils. The plasticity based on subloading and bounding surfaces is reformulated by incorporating temperature as an additional state variable, enabling the simulation of thermo-mechanical and thermo-hydraulic responses, respectively. The coupled thermo-hydro-mechanical behavior is subsequently described through appropriate hardening laws. The proposed formulation accounts for temperature-induced changes in the hydraulic boundary curves and enables the investigation of thermal plastic strains and their influence on the mechanical response of both normally consolidated and over consolidated soils. In addition, the model considers the coupled effects of temperature and matric suction, thereby providing a framework for simulating the thermo-hydraulic response of unsaturated soils. Finally, the predictive capability of the proposed model is evaluated against experimental results obtained from modified triaxial tests conducted on unsaturated soils under different thermal conditions.