The synthesis of transition metal-dinitrogen complexes and the stoichiometric transformation of their coordinated dinitrogen into ammonia and hydrazine have been the subject of considerable research, with a view to achieving nitrogen fixation under ambient conditions. Since a single example in 2003, no examples have been reported of the catalytic conversion of dinitrogen into ammonia under ambient conditions. The dimolybdenum-dinitrogen complex bearing PNP pincer ligands was found to work as an effective catalyst for the formation of ammonia from dinitrogen, with 23 equiv. of ammonia being produced with the catalyst (12 equiv. of ammonia are produced based on the molybdenum atom of the catalyst). This is another successful example of the catalytic and direct conversion of dinitrogen into ammonia under ambient reaction conditions. We believe that the results described in this Article provide valuable information with which to develop a more effective nitrogen-fixation system under mild reaction conditions.