AbstractNon-reciprocal electronic transport in a spatially homogeneous system arises from the simultaneous breaking of inversion and time-reversal symmetries. Superconducting and Josephson diodes, a key ingredient for future non-dissipative quantum devices, have recently been realized. Only a few examples of a vertical superconducting diode effect have been reported and its mechanism, especially whether intrinsic or extrinsic, remains elusive. Here we demonstrate a substantial supercurrent non-reciprocity in a van der Waals vertical Josephson junction formed with a T_d-WTe₂ barrier and NbSe₂ electrodes that clearly reflects the intrinsic crystal structure of T_d-WTe₂. The Josephson diode efficiency increases with the T_d-WTe₂ thickness up to critical thickness, and all junctions, irrespective of the barrier thickness, reveal magneto-chiral characteristics with respect to a mirror plane of T_d-WTe₂. Our results, together with the twist-angle-tuned magneto-chirality of a T_d-WTe₂ double-barrier junction, show that two-dimensional materials promise vertical Josephson diodes with high efficiency and tunability.