Manganese-based layered materials are promising owing to their resource-friendly, low-cost, non-toxic nature with high operational safety. Here, Na–Mn–O ternary layered metal oxide (Na2Mn3O7) was synthesized using a single-step conventional solid-state synthesis. The pure phase Na2Mn3O7 crystallizes in triclinic structure (s.g. P−1). It consists of Mn in 4+ oxidation state with electrochemically active Mn4+/Mn3+ redox center. The as-synthesized black powder worked as a robust cathode for the Na-, K-, and Li-ion half-cells. It delivered a reversible capacity of ~140, ~134, and ~160 mA h g−1, respectively, with Na, K, and Li metal as anode in half-cell architecture. Interestingly, Li- ion half-cell exhibited solid-solution-type (de)intercalation upon the variation of Li-ion concentration in Na2AxMn3O7 whereas Na and K-ion (de)intercalation involves two-phase redox reaction.