Heat accumulation and severe light scattering limit the applications of near-infrared phosphor-converted LEDs (NIR pc-LEDs) in the high-power field. Replacing phosphor encapsulation with Cr³⁺-doped glass-ceramics (GCs) provides an effective solution. However, obtaining transparent GCs with high thermal quenching resistance remains challenging. In this work, a novel Cr³⁺-doped MgNb₂O₆ GC was fabricated by co-melting and controlled crystallization using glass-forming and target-phase precursors. The resultant GCs possess acceptable transmittance and favorable thermal quenching resistance. By tuning the Mg/Nb ratio, a single MgNb₂O₆ crystalline phase was precipitated, and a two-step heat treatment optimized the GC transmittance. With nucleation temperature rising from 670 ℃ to 750 ℃ and crystallization temperature increasing from 820 ℃ to 960 ℃, crystallinity, grain size and luminous intensity gradually increase, whereas transmittance decreases monotonically. Cr³⁺ are proposed to simultaneously occupy Mg²⁺ and Nb⁵⁺ sites in MgNb₂O₆. Broadband NIR emission covering 600–1300 nm with a full width at half maximum (FWHM) of 210 nm is achieved, arising from intermediate and weak crystal fields and moderate electron-phonon coupling. After nucleation at 730 ℃ and crystallization at 940 ℃, the optimized GC shows a transmittance of approximately 50% and a high absorptivity of 60.5%. The GC exhibits favorable thermal quenching resistance, retaining 67.5% initial luminous intensity at 373 K. The NIR LED device integrated with the MgNb₂O₆:Cr³⁺ GC delivers an output power of 240.9 mW and a power conversion efficiency of 6.3%, demonstrating promising application prospects in night-vision illumination, food testing, biomedical and anti-counterfeiting fields.