Nickel sulfide thin films and nanocrystals stabilized with oleylamine ligands are prepared from two different nickel xanthates as single-source precursors, which decompose at approx. 180 °C, and are thereby converted into nickel sulfide. These nickel xanthates comprise branched alkyl moieties allowing the choice of a wide range of nonpolar organic solvents for the processing to nickel sulfide thin films as well as to nanoparticles. The crystal structures of both compounds show a typical square-planar coordination of the sulfur atoms of both xanthates to the nickel central atom. The thermal decomposition via the Chugaev reaction forming nickel sulfide was studied by thermal gravimetric analysis showing the reaction taking place at about 180 °C. Consequently, by thermally converting spin-coated metal xanthate films directly on the substrates in the solid state, thin films consisting of hexagonal nickel sulfide are formed. If the nickel xanthates are heated in an oleylamine solution, oleylamine-capped nickel sulfide nanocrystals are obtained, exhibiting hexagonal NiS as main phase and Ni₃S₄ as secondary phase. This is also reflected in a sulfur-rich composition of the synthesized nickel sulfide nanocrystals as observed from TEM–EDX analyses.