<p>Hydrogen interaction and diffusion in nanocrystalline Mg is crucial in determining its applicability in structural and storage purposes. Here, we have implemented molecular dynamics simulation to investigate the hydride formation, influence of H on mechanical properties, and hydrogen-induced embrittlement in NC Mg specimens. The results have shown that low H-content (approximately 1 to 2 at. pct H) aids in strengthening by facilitating the dislocation movement and the formation of stacking faults. However, with an increase in the H-content, the atomic interaction between Mg and H helps in the nucleation and development of MgH₂ hydride at the grain boundaries. The higher concentration of H also causes localized lattice distortion leading to amorphization, lower dislocation mobility, and embrittlement. Moreover, atomic observation has also shown that stress-induced mobility shifts the H-atom from the pre-existing octahedral voids to tetrahedral voids.</p> Graphical Abstract <p></p>