We report on the possibility for a spin valve effect driven by edge defect engineering of zigzag graphene nanoribbons. Based on a mean-field spin unrestricted Hubbard model, electronic band structures and conductance profiles are derived, using a self-consistent scheme to include gate-induced charge density. The use of an external gate is found to trigger a semiconductor-metal transitionincleanzigzaggraphenenanoribbons, whereasityieldsaclosureof thespin-splitbandgap in the presence of Klein edge defects. These features could be exploited to make novel charge and spin based switches and field effect devices.