Research interest in the thermo-mechanical behaviour of unsaturated soils is growing as a result of an increasing number of geomechanical problems involving both thermal and unsaturated effects. A new constitutive model dealing with partially saturated soils under non-isothermal conditions is presented through a unified and highly coupled constitutive approach. In the context of the elasto-thermoplasticity and the critical state theory, the so-called ACMEG-TS model uses the concepts of multi-mechanism and bounding surface theory. The generalized effective stress framework is adopted to represent the stress state in the soil. This model brings advancements on the thermo-hydraulic couplings that directly affect the mechanical behaviour of the materials. The constitutive relations based on the evolutions of the two key parameters (the preconsolidation pressure and the air-entry suction) make it possible to reproduce the main features of the thermo-mechanical behaviour of unsaturated soils. Theoretical aspects of the paper are supported by comparisons between numerical simulations and experimental results extracted from literature.