Developing blue-light-excited high-efficiency phosphor remains challenging for the fabrication of warm-white light-emitting diodes (LEDs) with an ultra-high color rending index (CRI). Here, the co-substitution of Ca2+-Hf4+ ion-pairs into a Y3Al5O12:Ce3+ phosphor, affords a novel, broadband, green-emitting CaY2HfAl4O12:2%Ce3+ garnet-type phosphor amenable to efficient blue light excitation. The structure, luminescent properties and blue-shift of this new material relative to a Y3Al5O12:2%Ce3+ phosphor have been extensively studied. Under 450 nm excitation, the optimum material exhibits high internal quantum efficiency (73.3%) and excellent thermal stability. Incorporation of the CaY2HfAl4O12:2%Ce3+ green phosphor into a prototype LED device delivers full-spectrum lighting with a high CRI (Ra = 97.2, R9 = 98.3) and low correlated color temperature (CCT = 3508 K). The resulting insight should aid the development of novel high-efficiency phosphors for full-spectrum warm-white LEDs with high-CRI value.