Poisson's ratio is an important parameter for the study of the behaviour of rocks in various contexts of rock engineering. Some studies have indicated that suction has an effect on Poisson's ratio of argillaceous rocks and that there is a non-linear response of this feature for other types of rocks during the loading process. Nevertheless, an assessment that couples the dependence of Poisson's ratio on stress and suction is still lacking. This study addresses this through a detailed analysis of axial and radial deformations during uniaxial compression tests on specimens at equilibrium under several different suction conditions using the moving point regression technique. Experimental results show a non-linear variation of Poisson's ratio with stress and that suction has a significant influence on it. The model proposed to couple the effect of suction and stress on Poisson's ratio of argillaceous rocks presents higher prediction performance.