Electronic, structural, and magnetic properties of Pt dichalcogenide monolayers are investigated using first-principle calculations. We find that hydrogenation lifts the spin degeneracy in narrow antibonding Pt $5d$ subband electrons and transforms the nonmagnetic semiconductors $\mathrm{Pt}{X}_{2}\phantom{\rule{0.16em}{0ex}}(X=\mathrm{S},\mathrm{Se},\mathrm{Te})$ into ferromagnetic metals, $\mathrm{Pt}{X}_{2}$-1H; neither strain nor thin-film edges are necessary to support the transition. The trend towards ferromagnetism is most pronounced for $X=\mathrm{S}$, decreasing with increasing atomic weight of the chalcogens.