In the present work, the improved shear-lag model based on a linear shear stress distribution in the substrates' thickness of a mixed-adhesive double-lap joint (MADLJ) has been developed to establish the shear stress profile along the joint length. A closed-form solution has been obtained and numerically validated by a 2D finite element simulation carried out on ABAQUS CAE commercial software. The analytical model has been then employed to conduct a parametric study where the influences of the stiff and soft adhesives Young moduli, their lengths as well as the joint's thickness on the maximum shear stress in the joint have been examined, and this for seven different substrate's thicknesses. Many key values of those parameters defining the transition of maximum shear stress from stiff to a soft region or defining an optimum stress or a limit value where the pure joint becomes advantageous along with their evolution with the adherents' thicknesses have been determined.