This manuscript investigates the thermal desorption behaviour of MgH₂/Mg(OH)₂ composites by means of thermal desorption spectroscopy. Besides the H₂O and H₂ desorption events due to Mg(OH)₂ dehydration and MgH₂ decomposition reactions, respectively, two additional H₂ desorption peaks arise at lower temperatures. These peaks are related to solid-state reactions between magnesium hydride and magnesium hydroxide through different channels. The low temperature H₂ peak (∼150 °C) is related to reaction between a H atom diffusing from MgH₂ and a surface OH group, whereas the intermediate temperature H₂ peak (∼350 °C) is due to an interface reaction between the hydride and the hydroxide. The present work supports the theory that the onset of the H₂ desorption coming from MgH₂ decomposition is controlled by an incubation process, consisting in the formation of catalytically active vacancies at the MgO/Mg(OH)₂ surface by dehydration. Possible ways to improve the H₂ desorption kinetics from MgH₂ are discussed in the light of the results obtained.