This paper describes a thermo-hydro-mechanical framework suitable for modelling the behaviour of unsaturated soils. In particular, this paper focuses on bentonite clay subjected to a thermo-hydromechanical load, as in the case of nuclear waste engineering barriers. The paper gives a theoretical derivation of the full set of coupled balance equations governing the material behaviour as well as an extended physical interpretation. Finally, a finite element discretisation of the equations and number of simulations verifying their implementation into a custom finite element code is provided. Some aspects of the formulation are also validated against experimental data.