<p>The controllable synthesis of two-dimensional multicomponent materials (2DMCMs) is of interest due to their dimension-related properties. However, traditional synthesis strategies are complex and unstable due to variable reaction pathways, which hinders material property studies. Here we report a space-confined chemical vapour transport strategy to synthesize high-quality 2DMCMs without phase separation and compositional inhomogeneity, by means of which we produce twelve types of transition metal phosphorous chalcogenides and their alloys (up to nine elements). By combining chemical vapour transport with confined growth space, a uniform and controllable vapour environment and selective lateral growth are realized. Precise composition control and consistency of components, including for high-entropy alloys, can thereby be achieved. Room-temperature ferroelectricity is observed in synthesized CuInP₂S₆ with clear electric hysteresis loops and switchable polarization, indicating that the high quality of synthesized crystals, and their properties, can be further tuned by introducing nickel heteroatoms. Additionally, the antiferromagnetic properties of transition metal phosphorous chalcogenides can also be tuned by introducing heteroatoms. Our method of synthesizing high-quality 2DMCMs and accurately regulating their components increases the availability of complex stoichiometric two-dimensional materials for exploring their composition–property correlation and underlying physical mechanisms.</p><p></p>