In the present paper transient as well as non-Darcian effects on laminar natural convection flow in a vertical channel embedded in a porous medium in the presence of uniform magnetic field applied normal to the flow region is studied. Forchheimer-Brinkman extended Darcy model is assumed to simulate momentum transfer within the porous medium. Approximate solutions are obtained using multi-parameter perturbation technique. Variations in the velocity field with Darcy number, Grashof number, kinematic viscosity ratio and variations in the temperature distribution are obtained and depicted graphically. Expression for the skin-friction and the rate of heat transfer at the channel walls are also derived and the numerical values for various physical parameters are presented in tabular form. (C) 2011 Elsevier Ltd. All rights reserved.