Ab initio total energy calculations using the full-potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient approximation (GGA) for the exchange-correlation potential have been performed to predict the structural, cohesive, electronic, and magnetic properties for tungsten oxycarbides. Two possible stoichiometries have been considered: WC1–xOx, formed by partial substitution of oxygen atoms for carbon in hexagonal WC, and WO3–xCx, which appear in the carburization process of WO3. The optimized lattice parameters, theoretical density, cohesive energies, as well as electronic densities of states have been obtained and analyzed for the first time. We have found that these two systems differ substantially: WC1–xOx behave as d metals, whereas WO3–xCx behave as sp metals. The unexpected d0-magnetism due to the C 2p ↓↑ spin splitting for some WO3–xCx solid solutions (SSs) was predicted. The chemical composition and O/C atomic ordering type are two main factors responsible for the properties of these materials.