We report the synthesis of the first carbide-hydride phase obtained in the family of equiatomic intermetallics RTX (R = rare earth, T = transition metal, X = p-block element) by insertion of light elements. We prepared the NdScSiC0.5H0.2 compound by solid-gas reaction, by exposing the carbide NdScSiC0.5 to 40 bars of H2 gas at 450 °C. It crystallizes in the La2Fe2Se2O3-type structure with H and C atoms occupying Nd4 tetrahedral and Nd2Sc4 octahedral interstices, respectively. The H site is only partly filled owing to the presence of Nd–C covalent bonding that prevents the formation of Nd–H bonding through antagonist effect. The carbide-hydride was characterized through magnetic measurements, specific heat and powder neutron diffraction. Remarkably, hydrogenation of the carbide provokes a quite drastic effect on the magnetic properties by changing the ground state from a ferromagnetic (TC∼70 K) to an antiferromagnetic one (TN = 10 K). The magnetic structure of NdScSiC0.5H0.2 consists of double layers of ferromagnetic Nd moments aligned along the c-axis and coupled antiferromagnetically along this axis. This magnetic structure results in a field-induced metamagnetic behaviour as pointed out by magnetisation isotherms.Read less <