Abstract: Strain-controlled low-cycle fatigue tests (with strain ratio of −1 and strain amplitudes of 0.4%, 0.6%, and 0.8%) and stress-controlled high-cycle fatigue tests (with stress ratio of 0.1 and maximum stresses of 600, 700, and 800 MPa) were conducted on TC4 ELI titanium alloy at room temperature to investigate its low-cycle and high-cycle fatigue performance. Based on the effective energy density, a unified fatigue life prediction model for both low-cycle and high-cycle fatigue conditions was developed and validated by using fatigue life data at room temperature. The results show that the low-cycle fatigue crack initiation was located on the test alloy surface under different strain amplitudes. The high-cycle fatigue crack initiated at the subsurface under the maximum stress of 600 MPa, and at the surface under the maximum stress of 700 and 800 MPa. 92% of the predicted low-cycle and high-cycle fatigue life data was in the error band of ±3.0, indicating that the developed fatigue life prediction model had high predictive accuracy.