High-repetition-rate laser pulses with large pulse energies have great application potential in various areas including telecommunications, sensing, material processing, etc. Here, we report the linear and nonlinear optical properties of solution-based transition-metal dichalcogenide NbSe₂ nanoparticles, and at the same time its application to mode-locked 2 μm fiber laser. The linear absorption of the NbSe₂ nanoparticles covers the near-infrared to the near mid-infrared regions, and decreases with increasing wavelength, showing a broadband operation potential. Nonlinear absorption measurement of the NbSe₂ nanoparticle gives a modulation depth of 6.5% and saturable intensity of 19 MW·cm^?2 at the wavelength of about 2 μm. The the NbSe₂ nanoparticles were transferred onto a gold mirror to fabricate a saturable absorber, with which a mode-locked thulium fiber laser was constructed and harmonic mode-locking was achieved. The mode-locked laser provides pulse energy of 3.36 nJ, pulse duration of 1.48 ns and repetition rate of 50.66 MHz. The laser wavelength is centered at 1 910.8 nm with a spectral bandwidth of 5.8 nm. The realization of dissipative-soliton mode-locking in the 2 μm fiber laser with NbSe₂ nanoparticles proves that NbSe₂ nanoparticles are good modulators for pulse generation in the 2 μm spectral region, and the integratable solution based nanoparticles hvae the potential of being new broadband nonlinear light modulators.