The photophysical, photochemical and electrochemical studies of a mixture of bipyridinyl ruthenium ([Ru II (bpy) 3 ] 2+ ) and manganese ([Mn II (L) 3 ] 2+ or [Mn 2 III,IV O 2 (L) 4 ] 3+ , L = bpy (2,2′-bipyridine) or dmbpy (4,4′-dimethyl-2,2′-bipyridine)) complexes have been investigated in CH 3 CN. Electrochemical oxidations of [Mn II (L) 3 ] 2+ are irreversible and lead, by subsequent chemical reactions, to the corresponding di-µ-oxo complex [Mn 2 III,IV O 2 (L) 4 ] 3+ with a good yield. These latter complexes can be then reversibly oxidized into the stable [Mn 2 IV,IV O 2 (L) 4 ] 4+ species. The luminescence lifetime of the excited state of the photosensitizer [Ru II (bpy) 3 ] 2+ * in the presence of variable concentration of manganese complexes has been determined. Using the Stern–Volmer equation, the quenching constant rate k q have been estimated. It appears that the [Mn II (L) 3 ] 2+ mononuclear complexes quench only very weakly the excited state [Ru II (bpy) 3 ] 2+ * since the magnitude of k q determined for the bpy and dmbpy complexes is about 10 7 M –1 s –1 . In contrast, a strong decrease of the luminescence lifetime is observed by addition of an increasing concentration of [Mn 2 III,IV O 2 (L) 4 ] 3+ . The k q values obtained for the bpy and dmbpy complexes are, respectively, 2.3 × 10 9 and 2.5 × 10 9 M –1 s –1 . The major quenching pathways of [Ru II (bpy) 3 ] 2+ * by those binuclear complexes of manganese are presumably energy transfer processes. Finally, the possibility of photocatalytic oxidation of [Mn II (L) 3 ] 2+ and [Mn 2 III,IV O 2 (L) 4 ] 3+ has been evaluated by continuous irradiation in the presence of the photosensitizer [Ru II (bpy) 3 ] 2+ and an aryl diazonium salt, ArN 2 + , playing the role of an irreversible electron acceptor. The photooxidation process transforming [Mn II (L) 3 ] 2+ into [Mn 2 III,IV O 2 (L) 4 ] 3+ by intermolecular electron transfers between photogenerated [Ru III (bpy) 3 ] 3+ and [Mn II (L) 3 ] 2+ occurs for the bpy and dmbpy complexes with a high efficiency. The subsequent photooxidation leading to [Mn 2 IV,IV O 2 (L) 4 ] 4+ is efficient only in the case of the dmbpy complex. The formation of those different species by electrochemical or photochemical ways has been demonstrated and quantified by coupled UV-visible absorption and EPR spectroscopy experiments. The efficiencies of the photoinduced oxidative processes have been correlated to the electrochemical data.