Cubic Mn_{2}Ga films with the half-Heusler C1_{b} structure are grown on V (001) epitaxial films. The phase is a soft ferrimagnet, with Curie temperature T_{C} = 225 K and magnetization M_{s}=280 kA m^{-1}, equivalent to 1.65μ_{B} per formula. Adding ruthenium leads to an increase of T_{C} up to 550 K in cubic Mn_{2}Ru_{x}Ga films with x = 0.33 and a collapse of the net magnetization. The anomalous Hall effect changes sign at x = 0.5, where the sign of the magnetization changes and the magnetic easy direction flips from in plane to perpendicular to the film. The Mn_{2}Ru_{0.5}Ga compound with a valence electron count of 21 is identified as a zero-moment ferrimagnet with high spin polarization, which shows evidence of half-metallicity.