Graphene-porphyrin nanohybrid materials with a direct covalent linkage between the graphene carbon network and the functional porphyrin unit have been successfully synthesized via a one-pot reductive diazotation approach. A graphite-potassium intercalation compound (KC8) was dispersed in THF, and different isolated porphyrin-diazonium salts were added. The direct covalent binding and the detailed characterization of the functional hybrid material were carried out by Raman spectroscopy, TG-MS, UV/vis, and fluorescence spectroscopy. LDI-ToF mass spectrometry was introduced as a new versatile and sensitive tool to investigate covalently functionalized graphene derivatives and to establish the composition of the respective nanohybrid materials.