We present the results of our spin polarized density functional study of the electronic and transport properties of defective graphene nanoribbons doped with boron or nitrogen atoms. We have analysed the formation energy, electronic band structure, magnetic charge density and quantum conductance of the doped defective graphene nanoribbon systems. We have demonstrated the half metallic behaviour of the doped defective graphene nanoribbons. The primary cause of the half metallic behaviour of this particular system is the charge transfer from carbon to dopant atoms. We have also shown that the band gap of the doped defective graphene nanoribbons decreases with the intensity of a transverse electrical field and reaches the state of a spin gapless semiconductor. The current–voltage characteristics of the doped defective graphene nanoribbons show the polarization of the spin current and have high spin filtering efficiencies.