The meta-xylylene biradical m-C8H8 represents a prototypical organic triplet that serves as a model compound for the test and refinement of quantum theoretical calculations and is a promising building block for organic molecule-based magnets. We used flash vacuum pyrolysis of 1,3-bisiodomethyl-benzene (m-C8H8I2) to produce m-C8H8 in the gas phase and photoelectron spectroscopy to probe the first two electronic states of the radical cation. The ionization energy was found to be (7.27±0.01) eV. From that, the heat of formation of the biradical is derived indirectly by investigating the C-I bond dissociation behavior of the precursor ion. We obtain ΔH_f;298K = (321.3±10) kJ/mol, which is slightly below the value of a previous study applying a different experimental approach.