Carbon-supported platinum-lanthanum (Pt-Ln) intermetallic compound (IMC) nanoparticles with high activity and robust stability have been demonstrated as promising cathode catalysts for proton-exchange membrane fuel cells. However, the preparation of Pt-Ln IMC catalysts needs high-temperature annealing treatment that inevitably causes nanoparticle sintering, resulting in significant reduction of the electrochemical surface area and mass-based activity. Here, we prepare small-sized M-doped Pt₅Ce (M = Ga, Cd, and Sb) IMCs catalysts via a low-melting-point metal doping strategy. We speculate that the doping of low-melting-point metals can facilitate the generation of vacancies in the crystal lattice through thermal activation and thus reduce the kinetic barriers for the formation of intermetallic Pt₅Ce catalysts. The prepared Ga-doped Pt₅Ce catalyst exhibits a higher electrochemical active surface area (81 m²·g_Pt^–1) and a larger mass activity (0.45 A·mg_Pt^–1 at 0.9 V) over the undoped Pt₅Ce and commercial Pt/C catalysts. In the membrane electrode assembly test, the Ga-doped Pt₅Ce cathode delivers a power density of 0.98 W·cm^–2 at 0.67 V, along with a voltage loss of only 27 mV at 0.8 A·cm^–2 at the end of accelerated stability test.