Field-assisted sintering technology (FAST), as a fast densification method with low process temperature, was used to manufacture self-passivating tungsten alloys (SPTAs) of W-Cr-Zr in this work. To clarify the behaviors of grain growth and Cr-rich phase precipitation under the action of electric current during the densification process, interrupted sintering at different temperatures (600–1000 °C) were performed. According to the viscous flow theory, the activation energy of W-Cr-Zr sample for densification is ~23 kJ/mol. The differential form of power law was adopted to evaluate the grain growth behavior. It is found that the W-Cr-Zr alloy consolidated by FAST has a low activation energy for grain growth of 82 kJ/mol. The Cr-rich phase could be confirmed by XRD spectra even when the sintering was interrupted at 600 °C. From the characterization of the cross-sectional microstructure, the Cr-rich phases tend to precipitate at sintering necks and defects (cracks/voids) in particle interiors. The low formation temperature of the Cr-rich phase is attributed to local overheating caused by local high electric current. This work provides significant insight into the mechanisms underlying the densification and the evolution of the microstructure of the SPTAs during the FAST process.