Rapid prototyping and design advancements in aviation gas turbine engine components are being made possible through the laser-fusion powder-bed additive manufacturing processes. However, with improvements in design, a comprehensive understanding of the fatigue performance of these components under realistic stress states characteristic of their in-service conditions is critical in ensuring their durability. Inconel 718 (IN718) is commonly employed as the substrate material for gas turbine engine components, and has been reported to yield improved axial mechanical properties when developed through the direct metal laser sintering (DMLS) process. However, the torsional fatigue properties of heat-treated Inconel 718 is yet unexplored. Given the nature of gas turbine engine components to endure multiaxial stresses (axial and torsional), this study is novel in that it reports the torsional fatigue properties of heat-treated DMLS Inconel 718. Completely reversed torsional fatigue tests under angle of twist control are performed on specimens manufactured along the horizontal, diagonal and vertical build orientations, providing the first set of torsional fatigue properties of additively manufactured heat-treated Inconel 718, contributing to a critical understanding of the performance of these components under cyclic shear.