Abstract The electronic and magnetic properties of magnetically doped transition-metal dichalcogenides are examined via first-principles calculations. With the confinement of wavefunctions in the two-dimensional space, substitutional doping of transition-metal elements can induce magnetism and spin splitting at band edges through the exchange interaction. Specifically, MX2 monolayers with M = (Mo, W) and X = (S, Se, Te) are explored for a range of dopants such as Fe, Mn, Co, Zn, Cd, V, Cu, and Sc. Among those studied, the results show that Fe and Mn may be promising candidates with large local magnetic moments. The exchange interaction in these two cases also appears to be Kondo-like. In addition, V and Sc are identified as the p-dopants for carrier-mediated magnetism despite their small magnetic moments. The effective exchange constants in Fe-doped and Mn-doped systems are deduced from the first-principles results and may be useful in the diluted systems, where the direct calculation is challenging.