Understanding the basic structure of the oxygen-evolving complex (OEC) in photosystem II (PS-II) and the water oxidation mechanism can aid in the discovery of more efficient and sustainable catalysts for water oxidation. In this context, we present evidence of the formation of a [(TPA)MnIV(O)(μ-O)CeIV(NO3)3]+ (2) complex (TPA = tris(pyridyl-2-methyl)amine) by adding aqueous ceric ammonium nitrate to an acetonitrile solution of the [(TPA)MnII]2+ (1) complex. This unique intermediate (2) was analyzed by using various spectroscopic techniques and electrospray ionization mass spectrometry. Remarkably, 2 closely mimics the structure of MnV(O)(μ-O)CaII(OH2) proposed in the OEC of PS-II. Notably, 2 reacts effectively with ferrocene derivatives, indicating that redox-active CeIV binding enhances the electron transfer efficiency. Additionally, 2 demonstrated the ability to perform oxygen atom transfer and hydrogen atom abstraction reactions. The discovery of this reactive [(TPA)MnIV(O)(μ-O)CeIV(NO3)3]+ species provides exciting opportunities for investigating the structure of the MnV(O)(μ-O)CaII(OH2) unit in the OEC.