<p>Hydrogen-based energy systems for transportation, power generation, and clean-energy applications have increased the demand for reliable structural materials. However, exposure to hydrogen significantly degrades the mechanical properties of materials through Hydrogen Embrittlement (HE), leading to premature crack initiation and catastrophic failure. In recent years, additive manufacturing (AM) has emerged as an advanced manufacturing approach for producing complex metallic components with improved characteristics, design flexibility, and tailored microstructures. However, the rapid solidification and repeated thermal cycling involved in AM processes result in residual stresses, porosity, anisotropy, and metastable phases, etc., which strongly influence hydrogen diffusion and embrittlement behaviour. This review presents a comprehensive overview of HE in AM-manufactured metallic materials fabricated using techniques such as Powder Bed Fusion (PBF) and Directed Energy Deposition (DED), along with the metallurgical characteristics of AM-produced alloys and their applications in hydrogen-related systems including fuel cells, electrolyzers, hydrogen storage devices, etc. Fundamental HE mechanisms, including Hydrogen Enhanced Localized Plasticity (HELP), Hydrogen Enhanced Decohesion (HEDE), Hydride Formation and Cleavage (HFC), and Adsorption Induced Dislocation Emission (AIDE), are critically examined in relation to AM-induced microstructures. Furthermore, recent studies on stainless steels, titanium alloys, nickel-based alloys, maraging steels, and high-entropy alloys are systematically reviewed to understand the influence of processing parameters, defects, post-processing treatments, and microstructural evolution on HE susceptibility. Finally, current research challenges, advanced characterization approaches, computational modelling, and emerging AI-assisted strategies for developing HE-resistant AM alloys are highlighted.</p>