We discovered a new compound MnCu₄In with its own hexagonal structure type (hP12-P6₃mc, ternary ordered derivative of the hexagonal MgZn₂-type) that becomes ferromagnetic at TC = 540 K. This transition temperature is higher than that found in the MnCu₂In and MnCu₂Sn alloys. In contrast, the homologous compound MnCu4Sn, which crystallizes in the cubic MgCu₄Sn-type, orders antiferromagnetically with TN = 110 K. The neutron diffraction studies show ferromagnetic spin orientation in the {101} plane in MnCu4In with a magnetic moment of 4.5 μB/Mn at 22 K, and a corresponding value of 4.7 lB/Mn in the antiferromagnetic MnCu₄Sn with propagation vector K = (1/2 1/2 1/2 ). The first-principles electronic structure calculations show that the unexpected difference in both magnetic and crystal structures of MnCu₄In and MnCu₄Sn is due to the difference in the Mn-3d bands and exchange interactions relating to different crystal anisotropy, coordination numbers, and interatomic distances.