A novel approach to selective electroless deposition of metal on non-conductive substrates was developed. Using an electroless copper process requires the non-conductive material to be catalysed prior to electroless deposition and this is typically carried out using a Pd-Sn colloidal catalyst. In the current work, a novel magnetic Fe3O4-Ag nanoparticle (NP) catalyst was used. The composite particles were obtained by a wet chemical method. The composition, particle size and crystal structure of the particles were confirmed by transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The magnetic properties were characterised by vibrating sample magnetometry whilst the catalytic activity towards formaldehyde oxidation (the key reaction in electroless copper deposition) was confirmed by cyclic voltammetry. Because this new catalyst is magnetic, a magnetic field gradient can be used to manipulate the catalyst NPs. A permanent magnet was attached to the constructed steel template so that a magnetic field gradient on the FR-4 laminate substrate surface was achieved. When the magnetic field was applied, the Fe3O4-Ag catalyst NPs were attracted only to the areas of maximum magnetic field gradient on the surface, leading to selective catalysation of the substrate. Subsequent electroless copper plating only occurred at the areas where the composite magnetic NPs were deposited, meaning that selective metallisation by applying a magnetic field was achieved. The width of the selectively metallised lines was 350±20 μm.