In this paper, the structural, electric and magnetic properties of transition metal (TM) doped monolayer Tl2S are investigated by means of first-principles methods The results show that all the considered TM atoms are strongly bonded to the Tl vacancy site. The magnetic moment, the dilute magnetic semiconductor and metal characteristics are varied depending on the specific TM atoms. The TM doped Tl2S (TM-Tl2S) (from Sc to Ni) systems have fractional magnetic moments changing from 0.539 mu(B) to 4.479 mu(B). However, Cu- and Zn-Tl2S systems exit the nonmagnetic ground states. The spin polarized metallic states are achieved by Sc, Ti, V, Mn and Fe doping, while spin polarized semiconducting states are realized by Cr, Co and Ni doping. The charge transfer, the total magnetic moment and the band gap obtained with PBE method are less than the values obtained by PBE + U, which suggests that the Hubbard U plays an important role in TM-Tl2S systems. In the case of two same types of TM atoms doped Tl2S systems, there exist AFM in Sc-, V-, Mn-Tl2S systems and FM only in Ti-Tl2S system. Interestingly, the Cr-, Fe-, Co-, Ni-Tl2S systems manifest paramagnetic. These findings may provide a new route for exploring two-dimensional diluted magnetic semiconductors experimentally and theoretically. (C) 2017 Elsevier B.V. All rights reserved.