The complex perovskite ThCu3Mn4O12 has been prepared at moderate pressures of 2 GPa. With respect to the parent compound CaCu3Mn4O12, the replacement of Ca2+ by Th4+ involves a double electronic injection that leads to a substantial increment of TC, up to 370 K. The crystal structure was refined in the space group Im3̄ from NPD data collected with λ = 1.33 Å at r. t. An additional NPD pattern recorded at 1.8 K with λ = 2.42 Å allowed to refine the magnetic structure, which displays a ferrimagnetic coupling between Mn3+/Mn4+ and Cu2+ spins, aligned along the c direction. The refined magnetic moments at the Mn and Cu substructures of 2.5 and −0.5 μB, respectively, account for the observed saturation magnetisation at 2 K, of 7 μB/f. u. A semiconducting behaviour is observed between 10 and 350 K which can be correlated with the appearance of a gap in the conduction band for the ~50% Mn3+/50% Mn4+ mixed valence observed in the B substructure of this perovskite.