Transparent Ce:lutetium aluminum garnet (Ce:Lu₃Al₅O₁₂, Ce:LuAG) ceramics have been regarded as potential scintillator materials due to their relatively high density and atomic number (Z_eff). However, the current Ce:LuAG ceramics exhibit a light yield much lower than the expected theoretical value due to the inevitable presence of Lu_Al antisite defects at high sintering temperatures. This work demonstrates a low-temperature (1100 ℃) synthetic strategy for elaborating transparent LuAG–Al₂O₃ nanoceramics through the crystallization of 72 mol% Al₂O₃–28 mol% Lu₂O₃ (ALu28) bulk glass. The biphasic nanostructure composed of LuAG and Al₂O₃ nanocrystals makes up the whole ceramic materials. Most of Al₂O₃ is distributed among LuAG grains, and the rest is present inside the LuAG grains. Fully dense biphasic LuAG–Al₂O₃ nanoceramics are highly transparent from the visible region to mid-infrared (MIR) region, and particularly the transmittance reaches 82% at 780 nm. Moreover, Lu_Al antisite defect-related centers are completely undetectable in X-ray excited luminescence (XEL) spectra of Ce:LuAG–Al₂O₃ nanoceramics with 0.3–1.0 at% Ce. The light yield of 0.3 at% Ce:LuAG–Al₂O₃ nanoceramics is estimated to be 20,000 ph/MeV with short 1 μs shaping time, which is far superior to that of commercial Bi₄Ge₃O₁₂ (BGO) single crystals. These results show that a low-temperature glass crystallization route provides an alternative approach for eliminating the antisite defects in LuAG-based ceramics, and is promising to produce garnet-based ceramic materials with excellent properties, thereby meeting the demands of advanced scintillation applications.