In the title compound, (C(20)H(20)N(4))[HgCl(4)], the Hg(II) ion is four-coordinated in a tetra-hedral environment defined by four chloride ions. The dihedral angle between the two phenyl rings is 32.83 (15)°. The protonated 1,1'-[(biphenyl-4,4'-di-yl)bis-(meth-yl-ene)]di-1H-imidazol-3-ium cations, showing a cis conformation, link the [HgCl(4)](2-) anions into an R(4) (4)(42) motif via N-H⋯Cl hydrogen bonds.