Lead halide perovskite nanowires (NWs) are emerging as a class of inexpensive semiconductors with broad bandgap tunability for optoelectronics, such as tunable NW lasers. Despite exciting progress, the current organic–inorganic hybrid perovskite NW lasers suffer from limited tunable wavelength range and poor material stability. Herein, we report facile solution growth of single-crystal NWs of inorganic perovskite CsPbX₃ (X = Br, Cl) and their alloys [CsPb(Br,Cl)₃] and a low-temperature vapor-phase halide exchange method to convert CsPbBr₃ NWs into perovskite phase CsPb(Br,I)₃ alloys and metastable CsPbI₃ with well-preserved perovskite crystal lattice and NW morphology. These single crystalline NWs with smooth end facets and subwavelength dimensions are ideal Fabry–Perot cavities for NW lasers. Optically pumped tunable lasing across the entire visible spectrum (420–710 nm) is demonstrated at room temperature from these NWs with low lasing thresholds and high-quality factors. Such highly efficient lasing similar to what can be achieved with organic–inorganic hybrid perovskites indicates that organic cation is not essential for light emission application from these lead halide perovskite materials. Furthermore, the CsPbBr₃ NW lasers show stable lasing emission with no measurable degradation after at least 8 h or 7.2 × 10⁹ laser shots under continuous illumination, which are substantially more robust than their organic–inorganic counterparts. The Cs-based perovskites offer a stable material platform for tunable NW lasers and other nanoscale optoelectronic devices.