A process is described for preparing a catalyst comprising at least one porous support and at least one metallic phase containing nickel and tin in a proportion such that the Sn/Ni molar ratio is in the range 0.01 to 0.2, said process comprising at least the following steps in succession: a) depositing nickel on at least said support in order to obtain a supported nickel-based monometallic catalyst; b) reducing said monometallic catalyst in the presence of at least one reducing gas; c) depositing, in the gas phase and in the presence of at least one reducing gas, at least one organometallic tin compound onto said reduced monometallic catalyst; and d) activating the solid derived from said step c) in the presence of at least one reducing gas.