Liquid-phase exfoliation of 2D transition metal dichalcogenides (TMDs) nanosheets in water is critical for their practical applications towards advanced thin-film electronics and ionotronics. We here report a versatile strategy for liquid-phase exfoliation of clay-like water-swollen TMD multilayers into delaminated 2D TMD nanosheets (including MoS2, WS2, MoSe2, etc.) with thin thicknesses of < 2 nm (e.g., 1.4 nm of MoS2) and high nanosheet concentrations. The delaminated TMD nanosheets can form stable colloidal dispersions in water with low Zeta potentials of <–32 mV over a month, and undergo phase transformation upon annealing from metallic 1 T phase to semiconducting 2H phase. These nanosheets can be coated on various circuit substrates as thin-film ionotronics; for example, an ionotronic device with an as-delaminated MoS2 channel achieves a high transconductance of 23 µS at a low operating voltage of −0.2 V. The delaminated TMDs dispersions are capable of co-dispersing other nanomaterials including 2D MXene and graphene, and 1D carbon nanotube and cellulose nanofibrils, forming stable colloidal co-dispersions in water offering a platform to fabricate multifunctional TMD-based nanocomposite films with high electromechanical integrity. Examples of MoS2/MXene films show an electronic conductivity of 1.66 × 105 S m−1 and a tensile strength of 70 MPa, higher than pure MoS2 films of 1.08 × 104 S m−1 and 55 MPa, and MoS2/CNF films with a higher tensile strength of 178 MPa and their hydrogel films presenting a mixed electronic/ionic conductivity of 18.2/0.16 S m−1. These outcomes promise potentially scalable applications in neuromorphic ionotronics, flexible electronics, energy storage, etc.