Two-dimensional (2D) layered Dion–Jacobson (D–J) phase organic–inorganic Sn-based perovskites show potential applications in field-effect transistors, similar to their Ruddlesden–Popper (R–P) counterparts; however, they have not attracted sufficient attention. In this work, we report on the investigations of 1,4-butanediamine tin iodide perovskite (BDASnI₄) and the demonstration of polymer-bottom-gated BDASnI₄ thin film field-effect transistors. First-principles calculations reveal that BDASnI₄ possesses a 2D layered D–J structure with small lattice distortions, which facilitates in-plane charge transport in the [SnI₆]⁴⁻ frameworks. Theoretical results and physical characteristics prove that the single BDA²⁺ layer eliminates the van der Waals gap in R–P perovskites, resulting in enhanced structural stability and a reduced quantum well effect. More importantly, the strong interlayer electronic coupling through the shortened apical I–I interactions improves the out-of-plane charge transport in BDASnI₄, which is regarded as a limitation for 2D R–P perovskites. BDASnI₄ transistors exhibit p-type high-performance with enhanced operating stability under ambient conditions. The hole mobility achieved in the champion device is 0.58 cm² V⁻¹ s⁻¹, approaching that of amorphous silicon. Our work provides theoretical and experimental bases for developing 2D layered D–J phase perovskites for field-effect transistors.