Luminescence-kinetics studies of Ce³⁺-doped GdP₃O₉ metaphosphate, which was prepared by a melt-solution technique, are performed using time-resolved luminescence spectroscopy techniques at T = 4.2–300 K. The processes of energy migration along the Gd³⁺ sub-lattice and energy transfer between Gd³⁺ and Ce³⁺ ions are investigated. At low temperatures, the emission of Gd³⁺ is caused by the radiative decay of its lowest-energy relaxed excited ⁶P_7/2 state, and the Gd³⁺ → Ce³⁺ energy transfer is absent. As the temperature increases, the thermally stimulated population of the higher energy ⁶P_5/2, ⁶P_3/2 levels of the Gd^{3+ 6}P_J-excited state takes place, which reveals itself in a higher energy shift of the Gd^{3+ 6}P_J → ⁸S_7/2 emission band. The phonon-assisted population of the Gd^{3+ 6}P_5/2 excited level at T < 150 K is suggested to be responsible for the increase in probability of energy migration along the Gd³⁺ sub-lattice followed by the Gd³⁺ → Ce³⁺ energy transfer. The more effective Gd³⁺ → Ce³⁺ energy transfer at T > 150 K takes place owing to the thermally stimulated population of the highest-energy ⁶P_3/2 excited level together with the lower energy shift of the Ce³⁺ 4f–5d₁ absorption band. Unlike the Gd³⁺ → Ce³⁺ transfer, the reverse Ce³⁺ → Gd³⁺ energy transfer is observed at any temperature.