[en] Highlights: • First-principles calculations are performed in series of TM doped MoS₂ in monolayer and bulk structures; • Both defects and defect complexes are considered using defects engineering; • Formation energies show the preferable sites of dopants and possible ferromagnetism can be obtained in TM doped MoS₂; • Experimental results show clear ferromagnetism in TM doped systems, confirming the computational results. First principle calculations are employed to calculate the electronic structure and magnetic properties of transition-metal doped MoS₂ considering the effects of defect/defect complex. It shows that pure MoS₂ with both Mo and S vacancy are nonmagnetic. Mn, Fe, Co and Ni substitution in Mo site all lead to spin polarized state. Considering defect complex, the results show that (TM_Mo + TM_Mo) defect complex has the lowest formation energy at high S pressure and prefers close to each other except for (Co_Mo + Co_Mo). Experimentally, we doped Mn, Co, Ni and Fe into MoS₂ single crystals. The doping leads to room temperature ferromagnetic ordering and clustering, agreeing well with the first principle calculations.