The work reports a new method for large-area growth of graphene films, which have been predicted to have novel and broad applications in the future. While chemical vapor deposition (CVD) is currently the preferred method, it suffers from a rather narrow processing window, and there is also much to be desired in the electrical properties of the CVD films. A new method for large-area growth of graphene films is reported to overcome the narrow processing window of the CVD method. A composite substrate made of a C-dissolving top (Ni) layer and a C-rejecting bottom (Cu) layer is designed, which evolves into a C-rejecting mixture, to autonomously regulate the C content at an elevated yet stable level at and near the surface over an extended duration. This “smart” substrate promotes graphene formation over a wide temperature-gas composition window, leading to reliable growth of wafer-sized graphene films of defined layer-thickness and superior electrical–optical properties. This “smart”-substrate strategy can also be implemented on Si and SiO2 supports, paving the way toward the direct fabrication of large area, graphene-enabled electronic and photonic devices.