Compared to the single crystal counterparts, the laser ceramic materials can achieve higher ion doping concentrations and thus have a considerable application potential in thin disc lasers as laser gain media. In this study, heavily doped Nd:YAG transparent ceramics with excellent optical quality were fabricated, and a watt level thin disc laser output with high efficiency without saturation was realised in 3.0 at.% Nd:YAG ceramic (500 μm thickness). However, the trends in transmission and laser performance of Nd:YAG transparent ceramics were inconsistent with the Nd3+ doping concentration owing to the sintering additive effect of the introduced Nd2O3, and the laser performance of a 2.5 at.% Nd:YAG transparent ceramics with 1.0 mm thickness was almost identical to that of 1.0 at.% samples. This study demonstrates that the ceramic laser gain medium is of great significance for miniaturising and integrating solid state lasers.