Research on graphene/nanostructure hybrid materials has been gaining momentum in recent years, with wide-ranging applications in gas sensing and detection. Specifically, noble metal decorated graphene-based novel structures were found to be extremely sensitive and selective owing to the synergistic effect of the compound configuration. In this article, recent developments in graphene/noble metal nanostructure hybrids and their promising potential in gas sensing applications has been highlighted. More significantly, an understanding of the electronic mechanism of gas sensing is presented with a specific emphasis on electron transfer and junctions effects at the graphene/nanostructure interfaces. Finally, the future research prospects of application of bi-metallic and tri-metallic nanostructure/graphene-based hybrids and the challenges in this new and rapidly growing domain are discussed.