A series of CoRMn-LDH (R = 1, 2, 3, 4, 5) was synthesized by the coprecipitation method. The formation of layered double hydroxide (LDH) phases is confirmed by powder X-ray diffraction (XRD) and infrared spectroscopy (FTIR). The energy-dispersive X-ray analysis (EDX) shows the total coprecipitation of Co and Mn. The X-ray photoelectron spectroscopy (XPS) result gives evidence of the joint presence of Co(II), Co(III), and Mn(III) in the LDH structures in proportion depending on the initial R value. The Rietveld refinement of the structure using the XRD data reveals that the sample with a Co/Mn ratio of 3:1 displays a pure LDH phase containing mainly Co(II) and Mn(III) with a M(II)/M(III) of nearly 2.1, in agreement with the X-ray absorption spectroscopy (XAS) results at the Co and Mn K-edges, strong hydrogen-bonding network involving CO32–/OH– charge-compensating anions in the interlayers. When compared with the other CoRMn-LDHs, the Co3Mn-LDH displays the best redox properties in an alkaline medium (0.1 M NaOH) and in a neutral pH (Tris buffer). An in-depth study of the Co3Mn-LDH obtained after electrochemical oxidation was also performed. The evolution of Co and Mn oxidation states under electrochemical oxidation was evidenced by XPS. Finally, the performance of the Co3Mn-LDH-modified electrode was determined for the electrocatalytic detection of hydrogen peroxide.