An olefin metathesis catalyst bearing a tridentate hemilabile N-heterocyclic carbene (NHC) ligand was synthesized and characterized. The solid-state crystal structure reveals coordination from all three donation sites of the NHC ligand, giving rise to a stable 18-electron complex. Catalytic activity in three standard metathesis reactions was demonstrated, revealing our catalyst to be particularly long lived and highly selective in the self-metathesis of 1-decene. Although the catalyst in this work initiates more slowly than its second-generation counterparts, it was shown to have high thermal stability, yielding peak performances at higher temperatures. The unique ligand framework of this catalyst may serve as a template for the synthesis of analogous catalysts with improved efficiencies.