We present ab initio pseudopotential–density-functional calculations for the electronic structure of the dilute magnetic semiconductor Mn$_x$Ga$_{1-x}$N , with a realistic $x = 0.063$ , in its ordered ferromagnetic phase. We find that the introduction of Mn results in the formation of a 100% spin polarized ∼1.5 eV -wide impurity band, primarily due to hybridization of Mn 3$d$ and N 2$p$ orbitals. This band renders the material half metallic and supports effective-mass transport within it. As such, Mn$_x$Ga$_{1-x}$N is a highly suitable material for spin injectors. Coupled with the previously reported high Curie temperature and inherent compatibility with GaN technology of this material, it emerges as a serious candidate for the next generation of spintronic devices.