In this paper, we present a new and powerful method to directly synthesize nanocrystalline metal hydrides from elementary components. This method consists of milling at high temperature under hydrogen with the addition of graphite to facilitate the first hydrogenation. We found that a synergetic effect is achieved and that it is possible to reach full hydrogenation in a very short time. This technique was tested on magnesium, which is known to be a material hard to activate. We found that full hydrogenation was realized after only about 1 h. This represents an order of magnitude reduction in processing time compared to any other methods known in the art.