Transparent phosphor ceramics have received increasing attention for high-brightness laser lighting, but commercially available phosphor ceramics are currently mainly limited to yellow YAG:Ce and green LuAG:Ce garnets, leaving a "cyan cavity" which is an obstacle to realizing full-color lighting. Achieving new phosphor ceramics capable of filling the cavity is a challenge. Herein, for the first time, cyan-green-emitting Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSS:Ce) transparent ceramics have been successfully developed by two-step sintering technique under vacuum. The as-prepared CSS:Ce ceramics present high relative density of 99.7% and optical transmittance of 71% in the cyan-green spectral region. It exhibits an efficient band emission peaking at 504 nm (under 450 nm excitation) with internal/external quantum efficiency of 91%/62%. Furthermore, it has excellent thermal stability with a thermal quenching temperature (T_0.5) of 838 K, approximately 100 K higher than that of LuAG:Ce ceramics (738 K). In addition, the CSS:Ce ceramics can withstand blue laser density of 45.6 W/mm² and meanwhile generates cyan-green light with a forward luminous flux of 813 lm and forward luminous efficacy of 162 lm/W. The CSS:Ce transparent ceramics exhibit excellent luminescence performance comparable to the commercial LuAG:Ce ceramics and could be a highly promising color converter for high-brightness laser lighting.