The structures, stabilities, and bonding mechanism of the square-planar doubly charged MXe₄²⁺ (M = Cu, Ag, Au) cations have been investigated at the UB3LYP and UMP2 theoretical levels. At the best theoretical estimate, the M–Xe bond lengths are calculated to be 266.2, 273.6, and 273.8 pm, and the corresponding binding energies with respect to M²⁺ and four xenon atoms are 771.49, 820.57, and 908.47 kJ mol^–1, respectively, along the series Cu – Ag – Au. Owing to an unusually high relativistic effect, gold evidently tends to be strongly bonded to the noble gas atoms in comparison with copper and silver. The electrostatic interactions play an important role in divalent noble-gas–noble-metal bonding. Apart from CuXe₄²⁺, the square-planar MXe₄²⁺ cations are stable enough to be prepared in experiments.