A nonoxidative addition pathway for the activation of NH bonds of ammonia Ru(II) complex is reported. The pincer complex 1 cleaves N-H bonds via metal-ligand cooperation involving aromatization of the pincer ligand without a change in the formal oxidation state of the metal. Electron-rich N-H bond substrates lead to reversible activation, while electron-poor substrates result in stable activation products. Isotopic labeling studies using ND3 as well as density functional theory calculations were used to shed light on the N-H activation mechanism.