The novel adduct 1,1,3,3-tetramethylguanidine–gallane, (Me₂N)₂CN(H)·GaH₃, has been prepared by the reaction of [(Me₂N)₂CNH₂]⁺Cl⁻ with LiGaH₄ in Et₂O solution. Its spectroscopic properties indicate a monomeric species with an unusually strong coordinate link between the imido function and GaH₃, an inference confirmed by the crystal structure at 150 K which also reveals significant secondary interactions through non-classical N–H⋯H–Ga bridges. Despite the intrinsic strength of the Ga–N bond, however, vaporisation at ca. 310 K occurs with partial dissociation, and decomposition via more than one pathway proceeds at temperatures >330–350 K to give a variety of products, including the free base, Me₂NH, H₂, and a novel gallium–nitrogen compound composed of a Ga₄N₄ cubane-like core bridged on three edges by –N{C(NMe₂)₂}GaH₂– units.