The Josephson diode effect originating from magnetochiral anisotropy has thus far been realized primarily in conventional two-dimensional electron gases. Here, we propose a graphene-based Josephson junction as a broadly gate-tunable platform for nonreciprocal supercurrent transport. We demonstrate that the nonreciprocal critical current not only reverses its sign when graphene is switched from n- to p-type doping via electrostatic gating, but its efficiency can also be continuously tuned from zero up to ∼ 40%. This gate-controlled polarity switching and efficiency modulation—unique to the chiral nature of Dirac fermions in graphene—has no counterpart in conventional semiconductor systems, positioning the graphene Josephson diode as a highly versatile component for advanced superconducting circuits.