Narrowband green-emission, combined with superior physicochemical stability and thermal performance, is regarded as a common pursuit in backlight display applications. However, mainstream phosphor-converted materials composed of resin or silicone resin easily encounter the dilemma of thermal decomposition and chemical corrosion for practical use. To overcome this problem, in this work, Mn2+/Mg2+ co-doped AlON ceramic is successfully realized with ultra-narrowband green-emission and high transparency. The luminescent property of AlON: Mn2+-Mg2+ ceramic exhibits narrowband green emission centered at 509 nm with a full width at half maximum of 36 nm, which is smaller than the corresponding powder counterpart (44 nm). Moreover, AlON: Mn2+-Mg2+ ceramic presents a wide color gamut (103.6%) and high color purity (74%). Concurrently, high transmittance of this ceramic, at 82%, unveils a potential innovation in the display technology field. This work may facilitate the development of narrowband green light-emitting converters based on AlON: Mn2+-Mg2+ transparent ceramics in large color gamut backlight display applications.