Barium zirconate-based high-temperature proton conductors (HTPCs) exhibit excellent chemical stability in atmospheres containing CO2 or water vapor. However, such HPTCs haven't been widely used as electrolyte materials for solid oxide fuel cells (SOFCs) due to their poor sintering activity. In this work, indium is selected as a dopant to improve the sintering activity of barium zirconate. BaZr0.8In0.2O3−δ (BZI) powders with a pure cubic perovskite structure are synthesized via a typical citric acid–nitrate gel combustion process. The SEM results show that BZI exhibits improved sintering activity compared to the state-of-the-art proton conductor BaZr0.8Y0.2O3−δ (BZY), and fully dense BZI pellets with increased grain size are obtained after sintered at 1600 °C in air. Moreover, BZI also keeps sufficiently high chemical stability as BZY. The electrical conductivity of BZI under various atmospheres is investigated by electrochemical impedance spectroscopy (EIS) in detail. The total conductivity achieves 1.0 × 10−3 S cm−1 at 700 °C in wet H2 (3% H2O). Dense BZI electrolyte films are successfully fabricated on the anode substrates by a dry-pressing method after sintered at 1400 °C for 5 h in air. Single cells with dense BZI electrolyte films are also assembled and tested to further evaluate the feasibility of BZI as an electrolyte material for proton-conducting SOFCs.