Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere, which not only results in property degradation but also significant equipment complexity and manufacturing costs. In this work, the ambient flash sintering behavior of reduced graphene oxide/3 mol％yttria-stabilized ZrO2 (rGO/3YSZ) composites utilizing rGO as both a composite component and a conductive additive is reported. When the sintering condition is carefully optimized, a dense and conductive composite can be achieved at room temperature and in the air within 20 s. The role of the rGO in the FS of the rGO/3YSZ composites is elucidated, especially with the assistance of a separate investigation on the thermal runaway behavior of the rGO. The work suggests a promising fabrication route for rGO/ceramic composites where the vacuum and furnace are not needed, which is of interest in terms of simplifying the fabrication equipment for energy and cost savings.