<p>This study investigates the combined effects of corrosion and hydrogen charging on the mechanical performance of two metallic materials—S45C carbon steel and STS316L stainless steel—exhibiting distinct corrosion behavior using indentation. Uniform corrosion was induced in S45C, while STS316L underwent pitting corrosion, followed by cathodic hydrogen charging. Hydrogen uptake was quantified via thermal desorption analysis, and mechanical properties were evaluated using nanoindentation and Vickers hardness tests. In S45C, corrosion reduced hydrogen uptake due to the formation of corrosion products such as iron oxides, leading to a transition from hydrogen-induced hardening to softening depending on the hydrogen content. In contrast, pitting corrosion in STS316L facilitated hydrogen absorption through grain boundary exposure, resulting in localized hydrogen accumulation. This enhanced the hydrogen-enhanced localized plasticity (HELP) mechanism and promoted microcrack formation, particularly in pit-damaged regions. The study reveals that corrosion not only alters hydrogen uptake behavior but also fundamentally modifies hydrogen–mechanical property relationships. These findings highlight the critical need to consider both hydrogen content and corrosion-induced structural degradation when evaluating the reliability of metallic components in hydrogen-rich, corrosive environments.</p> Graphical Abstract <p></p>