The single-source precursors of noble–ignoble nanoalloys are of a great interest since they can be used in many areas such as optical, biomedical, catalysis, magnetic and chemosensors. The new water-soluble double complex salts (DCSs) with aqua and oxalato ligands, [M(H 2 O) 6 ][Pd(Ox) 2 ]·nH 2 O (M = Co 2+ , Ni 2+ ; n = 2, 4; Ox = C 2 O 4 2− ), were obtained, structurally characterized (single-crystal XRD) and used as precursors for M–Pd nanoalloys. Complexes, intermediate and final thermolysis products were studied by simultaneous thermogravimetric analysis combined with mass spectrometry, powder XRD, in situ synchrotron powder XRD, IR and X-ray photoelectron spectroscopy. Decomposition in different atmospheres leads to formation of bimetallic solid solution M 0.5 Pd 0.5 (He, H 2 ) or a mixture of metal oxides (O 2 ). The catalysts M–Pd/TiO 2 (1% Pd) were prepared by the decomposition of DCSs deposited onto titania via wetness impregnation. The H 2 -made Ni-containing samples showed a high photocatalytic activity in CO oxidation reaction.