In the title compound, [Hg(C(14)H(13)N(4)O(3))Cl], the Hg(II) atom is four-coordinated by one O atom and two N atoms from a tridentate 1-(2-eth-oxy-phen-yl)-3-(4-nitro-phen-yl)triazenide ligand and one terminal chloride ion in a distorted square-planar geometry. In the crystal structure, the mononuclear complexes are linked into pairs through C-H⋯O and C-H⋯Cl hydrogen bonds as well as π-π and C-H⋯π stacking inter-actions. In addition, weak Hg-μ(6)-arene π-inter-actions [mean distance of 3.667 (2) Å] are present between these dimers. The π-π stacking inter-actions are between aromatic rings with a centroid-centroid distance of 3.884 (2) Å. Moreover, edge-to-face inter-actions are present between eth-oxy CH groups and aromatic rings with H⋯π distances of 2.81 Å.