Graphene-organic hybrid thin films are promising candidates for use as advanced transparent electrodes and high-performance photodetectors. In this work, we fabricated hybrid thin film structures consisting of graphene and either tetraphenyl-porphyrin (H2TPP) or metalloporphyrins such as aluminum (III) tetraphenyl-porphyrin (Al(III)TPP) and zinc tetraphenyl-porphyrin (ZnTPP). The optical and electrical characteristics of ultrathin photodetectors based on the graphene-organic hybrid layers were subsequently evaluated. A hybrid deposition system capable of both thermal evaporation and vapor phase metalation was employed to synthesize the tunable metalloporphyrin-based thin films. As a proof of concept, we successfully fabricated various graphene-based photodetectors via the simple and efficient vapor-phase metalation of porphyrin. This work may facilitate the development of new architectures for flexible graphene-organic devices.