Acceptor-doped barium cerate is considered as one of the state-of-the-art high temperature proton conductors (HTPCs), and the proton conductivity of such HTPCs is heavily dependent on the dopant. In this work, a codoping strategy is employed to improve the electrical conductivity and sinterability of BaCeO3-based HTPC. BaCe0.8SmxY0.2–xO3−δ (0 ≤ x ≤ 0.2) powders are synthesized by a typical citrate–nitrate combustion method. The XRD and Raman spectra reveal all the compounds have an orthorhombic perovskite structure. The effects of Sm and/or Y doping on the sinterability and electrical conductivity under different atmospheres are carefully investigated. The SEM results of the sintered BaCe0.8SmxY0.2–xO3−δ pellets indicate a significant sintering enhancement with increasing Sm concentration. BaCe0.8Sm0.1Y0.1O3−δ exhibits the highest electrical conductivity in hydrogen among the BaCe0.8SmxY0.2–xO3−δ pellets. Anode-supported BaCe0.8Sm0.1Y0.1O3−δ electrolyte membranes are also fabricated via a drop-coating process, and the corresponding single cell exhibits desirable power performance and durability at low temperatures. The results demonstrate that BaCe0.8Sm0.1Y0.1O3−δ is a promising proton conductor with high conductivity and sufficient sinterability for proton-conducting solid oxide fuel cells operating at reduced temperatures.