Nickel alloys are widely used in various applications that require high pressure and temperature resistance. With the increased use of hydrogen, several nickel-based components may be exposed to hydrogen gas. These applications include the nuclear industry, compressor components, aeronautical piping, and gas storage tanks. Inconel 718, known for its excellent mechanical properties at high temperature, has been extensively studied under hydrogen exposure, both in solution and under gas pressure. Despite its outstanding performance, this alloy is not commonly used in industrial applications due to its high cost, which makes it less suitable for industrial piping systems. Given these considerations, nickel alloy 625 presents itself as a promising alternative to Inconel 718 for such applications. Alloy 625 offers a more cost-effective solution while still providing good mechanical properties. However, unlike Inconel 718, only few studies has been published on the effect of H2 on fatigue performances. This lack of research is significant. The aim of this study is to investigate the performance of nickel alloy 625 when exposed to hydrogen gas under various fatigue crack growth conditions. The Hydrogen-Affected Fatigue Crack Growth is characterized by both the hydrogen gas pressure and the stress intensity factor range, . Specifically, the study focuses on the alloy’s sensitivity to hydrogen pressure, with fatigue crack propagation experiments conducted at pressures ranging from 0.3 to 30 MPa. A detailed analysis of fracture surfaces is provided to clarify the fracture modes and understand the mechanisms of hydrogen’s effect on fatigue crack growth. Furthermore, hydrogen susceptibility is discussed by comparing the hydrogen-affected fatigue crack growth rates observed in nickel alloy 625 to the typical response of Inconel 718 and austenitic steels as reported in the literature