Persistent luminescence (PersL) imaging without real-time external excitation has been regarded as the next generation of autofluorescence-free and heating effect-free optical imaging technique. However, in order to acquire improved spatial resolution and deep penetration depth, developing new near-infrared (NIR) persistent phosphors with intense and long duration PersL over 1000 nm is still a challenging task. Herein, by utilizing the persistent energy transfer from Ce<sup>3+</sup> to Er<sup>3+</sup>, we have successfully developed a series of garnet persistent phosphors of Gd<sub>3</sub>Al<sub>5-x</sub>Ga<sub>x</sub>O<sub>12</sub> (x=2.0, 2.5, 3.0, 3.5) doped with Ce<sup>3+</sup>, Cr<sup>3+</sup> and Er<sup>3+</sup> ions (GAGG:Ce-Cr-Er), which exhibit long yellow PersL ranging from 480 nm to 780 nm mainly due to the 5<i>d</i>-4<i>f</i> parity-allowed transition of Ce<sup>3+</sup>, and NIR PersL in the broad range from 1450 nm to 1670 nm due to the typical Er<sup>3+</sup>: <sup>4</sup>I<sub>13/2</sub>→<sup>4</sup>I<sub>15/2</sub> transition in garnets. Spectroscopic results of photoluminescence (PL), PersL, thermoluminescence (TL) and fluorescence/PersL decay curves of obtained garnet solid-solutions are discussed in detail, which suggest that GAGG:Ce-Cr-Er ganets with multi-wavelength PersL bands can be a potential candidate for longterm <i>in-vivo</i> optical imaging in the third biological window. Moreover, taking advantage of the Gd<sup>3+</sup> host ion with seven unpaired electrons in its 4<i>f</i> shell, enhanced positive contrast for magnetic resonance imaging (MRI) also can be expected using this material as a T1-weighted agent. Thus, the GAGG:Ce-Cr-Er persistent phosphor in the form of nano-particles possesses the possibility as a dual-mode medical diagnosis platform featuring both the deep tissue penetration for in vivo bio-imaging and the high spatial resolution for MRI.