AbstractTransition metal ions with d⁰ electronic states (Ti⁴⁺, Zr⁴⁺, Nb⁵⁺ and Ta⁵⁺) are widely investigated as functional materials. This work first illustrates that Sc³⁺ ion, long‐time ignored, displays a second‐order Jahn‐Teller (SOJT) effect similar to asymmetric oxide‐coordinated transition metal ions, thus providing a new ground to seek for asymmetric functional materials with enhanced performances. In Ba₃Sc₂(BO₃)₄, BO₃ groups are parallelly arranged, satisfying the ideal arrangement to produce large birefringence. Importantly, distorted octahedral ScO₆ with Sc³⁺ ion in its d⁰ electronic state enlarges birefringence unexpectedly up to 0.149 @ 550 nm, which is larger than previously reported borates containing solely BO₃, even to B₃O₆ units. Subsequently, the SOJT influence of distorted ScO₆ octahedra on birefringence is verified by a comparison between experimental data and theoretical calculations. In addition, Ba₃Sc₂(BO₃)₄ also displays a high transmittance in the range of 230 nm–3.5 μm with a UV cut‐off wavelength at 198 nm and a large laser induced damage threshold (2.7 GW/cm²), comparable to α‐BaB₂O₄. Above characteristics imply that the title compound may be a promising birefringent material.