This study of the crystal structure, electronic structure, and magnetic properties of the ζ₂-GaM (M = Cr, Mn or Fe) alloys is motivated by the recent reinvestigation of the crystallographic Al₈Cr₅ structure type of ζ₂-GaMn. The isostructural compounds ζ₂-GaFe and ζ₂-GaCr have been refined using X-ray powder diffraction as well as neutron powder diffraction for ζ₂-GaFe. Their structures have been refined using the space group R3̄m, with cell parameters a = 12.625(8) Å and c = 7.785(10) Å for ζ₂-GaCr and a = 12.4368(11) Å and c = 7.7642(10) Å for ζ₂-GaFe. Band structure calculations using the self-consistent, spin-polarized TB-LMTO method were performed to understand their electronic structure and magnetic properties. Band calculations show that from GaCr to GaFe the magnetic interactions change from weakly antiferromagnetic coupling to ferromagnetic coupling. Magnetic measurements confirm ferromagnetism for GaFe and show a weak paramagnetic response for GaCr.