Searching for viable field-emission structures with a stable emission current, high emission brightness, and low energy spread has always been highly demanded for the development of high-performance electron-optical instrumentation. In this work, a single-crystalline HfC nanowire emitter with an oxycarbide surface is investigated. This new emitter shows an excellent current stability with a fluctuation less than 1%/h, as well as a narrow energy spread and high emission brightness. It exhibits great potentials to be a practical electron source for experimental trials in electron microscopes.