The paper presents an experimental and modelling approach for the soil water retention behaviour of two deformable soils. The objective is to investigate the physical mechanisms that govern the soil water retention properties and to propose a constitutive framework for the soil water retention curve accounting for the initial state of compaction and deformability of soils. A granular soil and a clayey soil were subjected to drying over a wide range of suctions so that the residual state of saturation could be attained. The obtained soil water retention curves are synthesized and compared in terms of water content, void ratio, and degree of saturation, and are expressed as a function of the total suction. The observed features of behaviour are conceptualized into a modelling framework expressing the evolution of the degree of saturation as a function of suction. The proposed retention model makes use of the theory of elasto-plasticity and can thus be generalized into a hysteretic model applicable to drying-wetting cycles.