This article emphasizes the significance of entropy generation analysis and nonlinear temperature density relation on thermally stratified viscous fluid flow over a vertical plate embedded in a porous medium with a thermal dispersion effect. In addition, the convective surface boundary condition is taken into an account. By using the suitable transformations, the governing flow equations in dimensional form are converted into set of nondimensional partial differential equations. Then the local similarity and nonsimilarity procedures are applied to transform the set of nondimensional partial differential equations into set of ordinary differential equations and then the resulting system of equations are solved by Chebyshev spectral collocation method along with the successive linearization. The effect of pertinent parameters, namely, Biot number, mixed convection parameter, and thermal dispersion on velocity, temperature, entropy generation rate, and heat transfer rate are displayed graphically and the salient features are explored in detail.