An unsteady mixed convection flow over a moving vertical plate in a parallel free stream is considered to investigate the combined effects of buoyancy force and thermal diffusion in presence of Newtonian heating in which heat transfer rate from the surface is proportional to the local temperature and thermal radiation effects. It is assumed that the unsteadiness is caused by the time dependent free stream velocity as well as by the moving plate velocity. The governing boundary layer equations with boundary conditions are transformed into a non-dimensional form by a group of non-similar transformations. The resulting system of coupled non-linear partial differential equations is solved by an implicit finite difference scheme in combination with the quasi-linearization technique. Computations are performed and representative set is displayed graphically to illustrate the influence of the mixed convection parameter (lambda), Prandtl number (Pr), the ratio of free stream velocity to the composite reference velocity (epsilon), stream wise co ordinate (xi) and thermal radiation parameter (R) on the velocity and temperature profiles. The numerical results for the local skin-friction coefficient ((ReLCf)-C-1/2) and wall temperature (Gw(xi,0)) are also presented. The numerical results are presented in graphs revealing some interesting features of flow and heat transfer phenomena in this study. Present results are also compared with previously published works and are found to be in excellent agreement. (C) 2013 Elsevier Ltd. All rights reserved.