This work studies the Soret and Dufour effects on the boundary layer flow due to mixed convection heat and mass transfer over a downward-pointing vertical wedge in a porous medium saturated with Newtonian fluids with constant wall temperature and concentration. A suitable coordinate transformation is performed, and the obtained non-similar equations are solved by cubic spline collocation method. The effects of the Dufour parameter, Soret parameter, wedge angle parameter, mixed convection variable, and buoyancy ratio on the heat and mass transfer characteristics has been studied. The local Nusselt number is found to decrease when the Dufour parameter is increased. Moreover, an increase in the Soret number leads to a decrease in the local Sherwood number. For natural-convection-dominated regime, an increase in the Soret number leads to an increase in the local Nusselt number for buoyancy assisting flows and a decrease for buoyancy opposing flows. As the wedge angle parameter is increased, the local Nusselt number and the local Sherwood number increases for forced convection and forced-convection-dominated mixed convection. The wedge angle parameter is insignificant for natural convection or natural-convection-dominated mixed convection.