The electronic structure of the ground state of MgH₂²⁺ has been investigated using relativistically-corrected CCSD(T) in conjunction with ANO-RCC (Mg) and aug-cc-pVQZ (H) basis sets. The MgH₂²⁺ molecular potential energy surface possessed minima corresponding to both ¹A₁ and ¹∑g⁺ equilibrium structures (with a 1∑⁺ transition state). The ¹A₁ structure possessed Re and θe values of 2.0297 Å and of 22.09°, respectively. The higher-energy ¹∑g⁺ structure exhibited an Re value of 2.1658 Å. Property surfaces were constructed to calculate rovibrational energies and spectral line intensities for the ground states of (¹A₁)MgH₂²⁺ , (¹A') MgHD²⁺ and (¹A₁)MgD₂²⁺. For the vibration ground state of (¹A₁) MgH₂²⁺, the vibration-averaged Re and θe values were calculated to be 2.0209 Å and 22.53°, respectively. The A, B and C rotational constants were calculated to be 58.0, 2.21 and 2.11 cm⁻¹, respectively.