The synthesis of the reactive PN(CH) ligand 2‐di(tert‐butylphosphanomethyl)‐6‐phenylpyridine (1H) and its versatile coordination to a RhI center is described. Facile CH activation occurs in the presence of a (internal) base, thus resulting in the new cyclometalated complex [RhI(CO)(κ3‐P,N,C‐1)] (3), which has been structurally characterized. The resulting tridentate ligand framework was experimentally and computationally shown to display dual‐site proton‐responsive reactivity, including reversible cyclometalation. This feature was probed by selective H/D exchange with [D1]formic acid. The addition of HBF4 to 3 leads to rapid net protonolysis of the RhC bond to produce [RhI(CO)(κ3‐P,N,(CH)‐1)] (4). This species features a rare aryl CH agostic interaction in the solid state, as shown by X‐ray diffraction studies. The nature of this interaction was also studied computationally. Reaction of 3 with methyl iodide results in rapid and selective ortho‐methylation of the phenyl ring, thus generating [RhI(CO)(κ2‐P,N‐1Me)] (5). Variable‐temperature NMR spectroscopy indicates the involvement of a RhIII intermediate through formal oxidative addition to give trans‐[RhIII(CH3)(CO)(I)(κ3‐P,N,C‐1)] prior to CC reductive elimination. The RhIII–trans‐diiodide complex [RhI(CO)(I)2(κ3‐P,N,C‐1)] (6) has been structurally characterized as a model compound for this elusive intermediate.