A new oxide, LaMn3Ni2Mn2O12, was prepared by high-pressure and high-temperature synthesis methods. The compound crystallizes in an AA′3B2B′2O12-type A-site and B site ordered quadruple perovskite structure. The charge combination is confirmed to be LaMn3+3Ni2+2Mn4+2O12, where La and Mn3+ are 1:3 ordered at the A and A′sites and the Ni2+ and Mn4+ are also distributed at the B and B′ sites in an orderly fashion in a rocksalt-type manner, respectively. A G-type antiferromagnetic ordering originating from the A′-site Mn3+ sublattice is found to occur at TN ≈ 46 K. Subsequently, the spin coupling between the B-site Ni2+ and B′-site Mn4+ sublattices leads to an orthogonally ordered spin alignment with a net ferromagnetic component near TC ≈ 34 K. First-principles calculations demonstrate that the A′-site Mn3+ spins play a crucial role in determining the spin structure of the B and B′ sites. This LaMn3Ni2Mn2O12 provides a rare example that shows orthogonal spin ordering in the B and B′ sites assisted by ordered A-site magnetic ions in perovskite systems.