The sintering trajectory of the Ho,Pr:Y₂O₃ ceramics could be effectively adjusted by sintering in a flowing oxygen atmosphere instead of vacuum. The final-stage grain growth was significantly suppressed by the use of oxygen atmosphere presintering, resulting in smaller average grain sizes than those of samples sintered under vacuum, while the same relative density was achieved. After hot isostatic pressing (HIP), the oxygen presintered Ho,Pr:Y₂O₃ ceramics achieved excellent optical quality, with transmittance exceeding 80% at a wavelength of 680 nm. The codoping of Pr³⁺ as deactivating ions effectively depopulated the lower energy level ⁵I₇ during the Ho³⁺:⁵I₆ → ⁵I₇ transition, thereby making the Ho,Pr:Y₂O₃ ceramics more conducive to promoting population inversion in the 2.9 μm laser wavelength range.