Carbon nanomaterials demonstrate remarkable electrical, thermal, and mechanical properties that allow for a number of very important and exciting potential applications. In this review, we present an overview of the major advances in the organometallic chemistry of carbon nanotubes and graphene over the past decade. The review is focused only on carbon nanocomposites with metal–carbon bonds. We review and discuss various organometallic functionalization approaches and their role in the modification of carbon nanotubes and graphene nanomaterials. Particular attention is paid to reactions of carbon nanotubes with organolithium compounds and to organometallic η6 transition metal complexes with carbon nanotubes and graphene. We also consider the main applications of organometallic reactions of carbon nanomaterials for the preparation of polymer-grafted carbon nanotubes and the corresponding reinforced polymer composites and review the potential applications of transition metal derivatives of carbon nanomaterials in nanoelectronics, fabrication of high-mobility organometallic transistor devices, memory components, spintronics, and catalysis. Finally, we give a future outlook for the further development and applications of carbon nanomaterials containing metal–carbon bonds.