Magnesium hydride is considered as an ideal candidate for effective hydrogen storage due to its high gravimetric hydrogen capacity and accessibility. But its use as a commercial material is hindered by its relatively high operating temperatures and slow release/uptake kinetics. To solve this, we first synthesized Ni decorated graphene nanoplate (Ni/Gn) catalysts with highly dispersed metal nano-particles (NPs) via a facile method, then the as-prepared Ni/Gn catalysts were introduced by using the hydriding combustion synthesis and mechanical milling (HCS + MM) method to obtain Mg-based composites. Remarkable enhancement of hydrogen sorption rates has been found for these composites in the presence of Ni/Gn additives, especially for the Mg@Ni₈Gn₂ sample: a hydrogen absorption amount of 6.28 wt% within 100 s at 373 K and a hydrogen desorption amount of 5.73 wt% within 1800 s at 523 K. A rather low activation energy (71.8 kJ mol⁻¹) for the dehydrogenation of MgH₂ was determined in the same sample, indicating that relatively moderate temperatures are required to absorb/desorb hydrogen. The excellent hydrogen sorption rates of the composites are thought to be associated with the high dispersity of in situ formed nanometric Mg₂NiH₄ particles during the HCS + MM process. In addition, a microstrain-induced synergetic hydrogen sorption mechanism is proposed, being correlated by the local introduction of a Mg₂Ni nano-catalyst into the Mg matrix.