Abstract The structural and magnetic properties of Mn_1+x V_2-x O₄ (0 < x ⩽ 1) have been investigated by the heat capacity, magnetization, x-ray diffraction and neutron diffraction measurements, and a phase diagram of temperature versus composition was built up. For x ⩽ 0.3, a cubic-to-tetragonal (c > a) phase transition was observed. For x > 0.3, the system maintained the tetragonal lattice. Although the collinear and noncollinear magnetic transitions of V³⁺ ions were obtained in all compositions, the canting angles between the V³⁺ ions decreased with Mn³⁺-doping, and the ordering of the Mn³⁺ ions was only observed as x > 0.4. In order to study the dynamics of the ground state, the first principles simulation was applied to analyze not only the orbital effects of Mn²⁺, Mn³⁺, and V³⁺ ions, but also the related exchange energies.