Protonic ceramic electrochemical cells (PCECs) hold significant promise for efficient power generation and sustainable hydrogen production. However, their widespread adoption is hindered by the extreme sintering conditions required for electrolyte densification, often causing performance degradation due to Ba evaporation. Herein, microwave-driven vapor-phase diffusion sintering (MV-sintering) is introduced as an innovative approach for fabricating fully dense, stoichiometric electrolytes at a significantly reduced sintering temperature of 980 °C. This method demonstrates broad applicability across proton-conducting oxide electrolytes. The MV-sintered PCEC (MV-PCEC) achieves exceptional power densities of ≈2 W cm<sup>-2</sup> (600 °C) in fuel cell mode, alongside a remarkably high current density of 3.65 A cm<sup>-2</sup> at 1.3 V (650 °C) in electrolysis mode. Digital twin analysis underscores the MV-PCEC's enhanced microstructural features, including finer phase morphology, increased active sites, and improved gas transport. These findings provide critical insights into advancing sintering strategies for high-performance PCECs while mitigating challenges associated with conventional high-temperature processing.