The synthesis, purification, and isolation of mononuclear Ru complexes containing the tridentate dianionic meridional ligand pyridyl‐2,6‐dicarboxylato (pdc2−) of general formula [RuIII(pdc‐κ3‐N1O2)(bpy)Cl] (1III) and [RuII(pdc‐κ2‐N1O1)(bpy)2] (2II) (bpy is 2,2′‐bipyridine) is reported. These two complexes and their derivatives were thoroughly characterized through spectroscopic (UV/Vis, NMR) and electrochemical (cyclic voltammetry, differential pulse voltammetry, and coulometry) analyses, and three of the complexes were analyzed by single‐crystal X‐ray diffraction techniques. Under a high anodic applied potential, both complexes evolve towards the formation of Ru‐aquo/oxo derivative species, namely, [RuIII(pdc‐κ3‐N1O2)(bpy)(OH2)]+ (1‐O) and [RuIV(O)(pdc‐κ2‐N1O1)(bpy)2] (2‐O). These two complexes are active catalysts for the oxidation of water to dioxygen and their catalytic activity was analyzed through electrochemical techniques. A maximum turnover frequency (TOFmax)=2.4–3.4×103 s−1 was calculated for 2‐O.