Graphene is extremely promising for next-generation spintronics applications; however, realizing graphene-based room-temperature magnets remains a great challenge. Here, for the first time, we demonstrate that robust room-temperature ferromagnetism with TC up to ~400 K and saturation magnetization of 0.11 emu/g (300 K) can be achieved in graphene by embedding isolated Co atoms with the aid of coordinated N atoms. Extensive structural characterizations show that square-planar Co-N4 moieties were formed in the graphene lattices, where atomically dispersed Co atoms provide local magnetic moments. Detailed electronic structure calculations reveal that the d-p orbital hybridization between the embedded Co and matrix N/C atoms generates spin polarization for the delocalized N/C 2pz electrons and consequently enhances the long-range coupling through Stoner ferromagnetism. This work provides an effective means to induce room-temperature ferromagnetism in graphene and may open the possibilities for developing graphene-based spintronics devices.