Cs3Mn2O4, a new member of the small family of ternary manganese (II/III) mixed-valent compounds, has been synthesized via the azide/nitrate route and studied using powder and single crystal X-ray diffraction, magnetic susceptibility measurements and density functional theory (DFT). Its crystal structure (P2(1)/c, Z = 8, a = 1276.33(1) pm, b = 1082.31(2) pm, c = 1280.29(2) pm, beta = 118.390(2)degrees) is based on one-dimensional MnO21.5- chains built up from edge-sharing MnO4 tetrahedra. The title compound is the first example of an intrinsically doped transition metalate of the series A(x)MnO(2), (A = alkali metal) where a complete 1:1 charge ordering of Mn2+ and Mn3+ is observed along the chains (-Mn2+-Mn3+-Mn2+-Mn3+-). From the magnetic point of view it basically consists of ferrimagnetic MnO2 chains, where the Mn2+ and Mn3+ ions are strongly antiferromagnetically coupled up to high temperatures. Very interestingly, their long-range three-dimensional ordering below the Neel temperature (T-N) similar to 12 K give rise to conspicuous field dependent magnetic ordering phenomena, for which we propose a consistent picture based on the change from antiferromagnetic to ferromagnetic coupling between the chains. Electronic structure calculations confirm the antiferromagnetic ordering as the ground state for Cs3Mn2O4 and ferrimagnetic ordering as its nearly degenerate state.