The growth of high‐quality halide perovskite single crystals is imperative to study their intrinsic physical properties and to realize high‐performance optoelectronic devices. Here, a room‐temperature solvent evaporation‐induced crystallization (RTSEIC) method is reported based on Le Chatelier's principle, which provides a general strategy to grow halide perovskite single crystals including 3D, 2D, 1D, and 0D, and either hybrid or all‐inorganic halide perovskites. Taking 2D n‐BA2PbBr4 (n‐BA = butylammonium) as an example, the room‐temperature crystallization kinetics is demonstrated. The centimeter‐sized n‐BA2PbBr4 single crystals exhibit an extremely small full width at half maximum (FWHM) of 0.024° in (0 0 2) plane rocking curve and a small trap density of 2.74 × 1010 cm−3. The superior crystalline quality endows the n‐BA2PbBr4 single crystal ultraviolet photodetectors with recorded performance among reported n‐BA2PbBr4 ultraviolet photodetectors, demonstrating a detectivity reaching 1.8 × 1013 Jones, a fast response time of 55 µs and a high on‐off ratio of 104. The low‐cost, simple, general, and efficient RTSEIC method is anticipated to promote the blossoming of halide perovskites single crystals.