The hydrogen embrittlement behavior of heat-treated Alloy 718 fabricated by laser powder bed fusion was fundamentally investigated under electrochemical hydrogen charging. The H transitioned the fracture mode from ductile dimpled to transgranular fracture with a flat fracture surface. Crystallographic analysis showed that H promoted the dislocation slip band, and the resulting concentrated strain and H along the slip planes caused cracking regardless of the distribution of additive manufacturing (AM) microstructural features such as sub-grain boundaries. In addition, thermal desorption spectroscopy and H-permeation tests indicated that the AM microstructural features after heat treatment only slightly influenced the H trapping and diffusion.