Currently, the preparation of MgAl_1.9Ga_0.1O₄ transparent ceramics which possess excellent optical properties, is still relying on combining aqueous gel-casting and prolonged pressureless pre-sintering. In this work, MgF₂ was used as a sintering additive, and densification process of pressureless pre-sintering was adjusted by a transient liquid phase. MgAl_1.9Ga_0.1O₄ transparent ceramics with different sizes were prepared by dry pressing, pressureless pre-sintering, and hot isostatic pressing treatment. The effects of MgF₂ additive on microstructure, optical, and mechanical properties of the samples were systematically analyzed. The results indicated that MgF₂ melted at ~1230 ℃, contributing to increase of density and grain size of the pre-sintered body, while the residual MgF₂ was oxidized to MgO and dissolved into the MgAl_1.9Ga_0.1O₄ lattice in the subsequent sintering process. The 2.04 mm thick transparent ceramic sample with 0.20% (in mass fraction) MgF₂ has an in-line transmittance of 76.5%-83.4% in the UV and visible regions. Moreover, the sample has high optical quality with low scattering on incident light. In addition, the characteristic flexural strength of this ceramics is 167.1 MPa, which is close to that of the fine-grained MgAl₂O₄ transparent ceramics, but the Weibull modulus (8.81±0.29) is higher. This study provided a new option for the preparation of large MgAl_1.9Ga_0.1O₄ transparent ceramic materials with good optical properties.