TbCu3Mn4O12 perovskite has been prepared in polycrystalline form under moderate pressure conditions of 2 GPa, in the presence of KClO4 as oxidizing agent. This material has been studied by X-ray and neutron powder diffraction (XRD and NPD) and magnetotransport measurements. The crystal structure is cubic, space group Im3̄ (No. 204), with a = 7.2668(1) Å at room temperature (RT). This compound presents a ABO3 perovskite superstructure, where the A positions are occupied by Tb and Cu, ordered in a 1:3 arrangement, giving rise to the body centering of the unit cell. At the B positions, Mn adopts a mixed oxidation state of 3.75+; MnO6 octahedra are considerably tilted by 19°, due to the relatively small size of the A-type cations. TbCu3Mn4O12 is ferrimagnetic below TC = 395 K:  the magnetic structure, studied by NPD, reveals that Mn and Cu spins are ordered below TC in an antiparallel arrangement. Additionally, below 100 K the Tb magnetic moments also participate in the magnetic structure, becoming antiferromagnetically coupled to Mn spins. This arrangement can be broken under the presence of an external magnetic field, inducing a turnover of the Tb magnetic moments, which then become parallel to the Mn moments. The mixed valence state created at the Mn sublattice is responsible for the observed metallic behavior; a negative magnetoresistance of 25% is achieved at 5 K for H = 9 T.