Transition metal dichalcogenides (TMDs) are one of the most explored classes of two-dimensional materials. The experimental routes for synthesis and device construction in these materials are well established allowing future applications. Materials with topological phases of matter present the possibility of electronic transport with long coherence length, due to the protection of their surface states by time-reversal symmetry. Such systems allow for the development of low-power electronics and new device functionalities. We show that energetically favorable defects in TMDs, Hg doping, and chalcogen vacancies, introduce topological states in their semiconductor gap. The transition from trivial to non-trivial occurs at a critical concentration of defects and is robust against disorder.