We report the first observation to our knowledge of room-temperature continuous-wave laser operation of a ${\mathrm{Pr}}^{3+}:\mathrm{K}{\mathrm{Y}}_3{\mathrm{F}}_{10}$ single crystal at $644.5\mathrm{nm}$ , pumped by a blue GaN laser diode emitting at $446\mathrm{nm}$ . With a 2.5% transmission output coupler and a nonoptimized optical cavity, an output power of $39\mathrm{mW}$ was obtained at $644.5\mathrm{nm}$ with a laser threshold of $125\mathrm{mW}$ and a differential slope efficiency of 23%.