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.