Cr3+-doped phosphors have recently gained attention for their application in broadband near-infrared phosphor-converted light-emitting diodes (pc-LEDs), but generally exhibit low efficiency. In this work, K2Ga2Sn6O16:Cr3+ (KGSO:Cr) phosphor was designed and synthesized. The experimental results show that the Cr3+-doped phosphor exhibited broadband emissivity in the range 650-1300 nm, with a full width at half maximum (FWHM) of approximately 220-230 nm excited by a wavelength of 450 nm. With the co-doping of Gd3+ ions, the internal quantum efficiency (IQE) of the KGSO:Cr phosphor increased from 34% to 48%. The Gd3+ ions acted neither as activators nor sensitizers, but to justify the crystal field environment for efficient Cr3+ ions broad emission. The Huang-Rhys factor decreased as the co-doping of Gd3+ ions increased, demonstrating that the nonradiative transitions were suppressed. An efficient strategy for enhancing the luminescence properties of Cr3+ ions is proposed for the first time. The Gd3+-co-doped KGSO:Cr phosphor is a promising candidate for broadband NIR pc-LEDs.