Solvothermal methods to synthesize cerium-doped YAG nanoparticles (YAG:Ce³⁺ NPs) generally require relatively long heating times (t_h ≥ 1 h) and temperatures close to 300 °C. In this work, we report a rapid solvothermal synthesis (t_h = 5 min) leading to well-crystallized and highly monodisperse YAG:Ce³⁺ NPs of about 30 nm diameter by heating mixed yttrium, aluminium and cerium carbonate precursors in an autoclave at 300 °C using a 1,4-butylene glycol–water mixture as solvent. The as-prepared YAG:Ce³⁺ NPs showed a broad emission band in the green–yellow range having maximum intensity at 550 nm upon blue or UV excitation. The effect of heating time and Ce³⁺ concentration on structural, morphological and optical properties of YAG:Ce³⁺ NPs has been systematically studied by X-ray powder diffraction, transmission electron microscopy, FT-IR spectroscopy, energy dispersive spectroscopy and room temperature photoluminescence experiments. The combination of low Ce³⁺ doping concentration and short heating time plays a crucial role in the good optical properties of the obtained YAG:Ce³⁺ NPs. The particles hold good potential to be applied in solid-state lighting or used as coating for display system applications.