In the title compound, [HgCl₂(C₁₆H₂₈N₂Se)], the primary geometry around the Se and Hg atoms is distorted trigonal–pyramidal and distorted square-pyramidal, respectively. The distortion of the molecular geometry in the complex is caused by the steric demands of the ligands attached to the Se atom. The Hg atom is coordinated through two chloride anions, an N atom and an Se atom, making up an unusual HgNSeCl₂ coordination sphere with an additional long Hg...N interaction. Intermolecular C—H...Cl interactions are the only identified intermolecular hydrogen-bonding interactions that seem to be responsible for the self assembly. These relatively weak C—H...Cl hydrogen bonds possess the required linearity and donor–acceptor distances. They act as molecular associative forces that result in a supramolecular assembly along the b-axis direction in the solid state of the title compound.