This study presents the results of an experimental investigation conducted to assess the temperature effects on shear stress–strain behaviour and shear strength parameters of red clay and its interface with the geostructure under different normal stresses (50, 100, 200, and 400 kPa). A modified direct shear test apparatus, capable of handling temperatures up to 50 °C, was used in this study. The experimental program includes shearing the red clay and red clay–structure interface at different temperatures (2, 15, 38 °C) and after subjecting it to different heating–cooling cycles. The test results in this study and the previous studies in the literature indicated that the temperature has insignificant effects on the friction angle of clay and clay–structure interface. However, the temperature effect on the cohesion of clay and the adhesion between the clay and structure depends on the normal stress level and history. A new conceptual understanding for the possible temperature effect on the clay–structure interface was introduced in this study and it was used to interpret the different interface test results in the literature.