Due to their unusual electronic structure, the biradical m-benzyne, C₆H₄, and its cation are of considerable interest in chemistry. Here, the photoion mass-selected threshold photoelectron spectrum of the m-benzyne biradical is presented. An adiabatic ionization energy of 8.65 ± 0.015 eV is derived, while a vibrational progression of 0.10 eV is assigned to the ν₉⁺ ring breathing mode, in excellent agreement with computations. The experimental spectrum was reproduced well by Franck-Condon spectral modeling of the ²A₁ ← X ¹A₁ transition, in which the cation retains a monocyclic C₆ framework. The energetically close-lying bicyclic ²A₂ cation state exhibits low Franck-Condon factors, due to the large change in geometry, and thus cannot be observed.