jats:p Design of retaining walls in clay is typically based on ultimate limit state calculations to prevent collapse, with arbitrary factors of safety used to limit deformations. These factors of safety do not take into account the different rates of strength mobilisation in the wide variety of clays found worldwide. As there is substantial uncertainty in this approach, conventional design tends to lead to excessive conservatism with associated high cost. The novel analysis procedure based on the fraction of the strength of soil mobilised for a given wall displacement developed here allows rapid assessment of wall deformations and stresses by way of a simple two-parameter constitutive model which can be easily calibrated using conventional triaxial data. The model is validated based on field and model case histories with a variety of different clays and propping conditions and is shown to exhibit good performance in predicting the behaviour of published case histories based on soil parameters extracted from previously published soil test data. This novel analysis provides for the first time a route for practising engineers to carry out fast, efficient design at early stages of the design process by considering many potential wall geometries without the computational overhead of complex finite-element or finite-difference numerical models. </jats:p>