The electronic structure and potential curves for the lowest states of the Ni₂⁺ cation have been studied using multiconfigurational SCF theory (CASSCF) combined with second-order perturbation theory (CASPT2) and non-orthogonal CI. The wavefunctions for the so-called sigma-hole states break symmetry at all internuclear distances longer than equilibrium. CASSCF and CASPT2 calculations were first perfomed using C_2v symmetry. Full symmetry was restored by mixing two symmetry related CASSCF wavefunctions. Ni₂⁺ has a ⁴(Sigma)_u^- ground state with a computed bond energy of 2.47 eV and a bond distance of 2.19 Å. The approach leads to a somewhat large binding energy due to double counting of the resonance energy. An estimate of the error yields a binding energy of slightly less than 2.4 eV. Calculations using D_2h symmetry give a binding energy (D₀) of 2.25 eV and a bond distance of 2.22 Å, in apparent agreement with experiment (D₀=2.25 eV, r_e=2.22 Å), indicating that the symmetry breaking error is independent of the internuclear distance.