2D layer-structured nanomaterials have attracted much attention owing to their excellent optical, electrical, and magnetic properties. In this study, a novel 2D zirconium tritelluride (ZrTe₃) nanosheet material is prepared. The nonlinear saturated absorption characteristics of the ZrTe₃ nanosheets are studied using the double-equilibrium detection method. The saturation intensity and modulation depth are 100.6 MW cm⁻² and 3.3%, respectively. A saturable absorber (SA) based on ZrTe₃ is used in a harmonic passive mode-locking erbium-doped fiber laser for the first time. The results show that when the pump power is 50 mW, mode-locking with a fundamental frequency of 5.82 MHz is achieved. The pulse width, center wavelength, 3 dB bandwidth, and signal-to-noise ratio (SNR) are 1.44 ps, 1563.7 nm, 2.31 nm, and 76 dB, respectively. With an increase in pump power, a high repetition rate of 483.1 MHz, corresponding to the 83-order harmonic mode-locked, is obtained at a pump power of 310 mW. The pulse width, 3 dB optical spectral width, and SNR are 1.302 ps, 3.14 nm, and 67 dB, respectively. This reveals that ZrTe₃ nanosheets are excellent photonic materials that can be used to generate high-repetition-rate pulse lasers and have great application potential in ultrafast photonics.