<p>Accurate characterization of nonlinear creep behavior in rocks is critical for understanding geological hazards and preventing geotechnical disasters. Most existing creep damage coupled models fail to capture the nonlinear evolution of creep damage. As a result, they cannot describe nonlinear creep behavior with a single set of parameters. To address this gap, a unified statistical damage evolution equation is derived to describe the damage growth during both instantaneous and constant loading stages. In addition, a novel four-element fractional viscoelastic–viscoplastic (FVEVP) constitutive law is introduced. By integrating the FVEVP constitutive law into the unified statistical damage evolution equation, a unified nonlinear creep damage coupled model is proposed to capture both the stress- and time-dependent mechanical behavior of rocks. A detailed procedure for identifying the model parameters is presented. The validity and applicability of the proposed model are verified by fitting experimental data from laboratory creep tests, where microscopic observations are conducted using acoustic emission (AE) and nuclear magnetic resonance (NMR) techniques. The results demonstrate that the proposed model accurately captures the nonlinear mechanical response during the instantaneous loading stage, as well as the nonlinear creep damage evolution characteristics and nonlinear creep deformation during constant loading stage. Compared to existing models, the proposed model effectively characterizes creep behavior across varying stress levels with a single set of parameters and accounts for the effect of initial damage on creep behavior.</p>