The asymmetric unit of the title complex, [Ni(C12H8N2)3][NiCl3(C7H12N2S)]2·2CH3CN, consists of one anion, one-half of a cation and one acetonitrile molecule. The NiII atom in the [Ni(phen)3]2+ cation (phen is 1,10-phenanthroline) lies on an inversion centre in an octahedral environment, whereas in the [NiCl3(tm)]− anion [tm is 1-tert-butylimidazole-2(3H)-thione], the geometry is distorted tetrahedral. In the crystal structure, intermolecular C—H⋯Cl hydrogen bonds and π–π stacking interactions (centroid–centroid distance = 3.52 Å) lead to the formation of a three-dimensional framework. One of the methyl groups of the tert-butyl group of N-tert-butyl-2-thioimidazole is disordered between two equally populated positions.