The paper presents the numerical investigation of the convection heat and mass transfer in a hydromagnetic Carreau fluid past a vertical porous plate in presence of thermal radiation and thermal diffusion. The non-linear partial differential equations governing the flow are transformed in ordinary differential equations using the usual similarity method and the resulting similarity equations are solved numerically using Runge-Kutta shooting method. The results are presented as velocity, temperature, and concentration profiles for different values of parameters entering in the problem. The effects of suction, magnetic field, thermal radiation, and thermal diffusion on the skin friction, rate of heat transfer and mass transfer are presented numerically in tabular form.