Lead-halide perovskites have made great advances in direct X-ray detection due to their large mobility-lifetime (μτ), strong X-ray absorption, and ease of synthesis, but the presence of toxic lead and high ionic migration severely limit their commercial applicability and operational stability. In this study, we substituted toxic Pb²⁺ with Bi³⁺ and Mn²⁺ for preparing eco-friendly two-dimensional lead-free perovskite Cs₄MnBi₂Cl₁₂ single crystal (SC) by a hydrothermal method. The SC possesses smooth surface, good crystallinity, high μτ (1.8 × 10⁻³ cm²·V⁻¹), and excellent stability. Therefore, the X-ray detector prepared with the Cs₄MnBi₂Cl₁₂ SC achieved an extraordinary sensitivity of 2.1 × 10³ μC·Gy_air⁻¹·cm⁻² and a low limit-of-detection of 1.05 nGy_air·s⁻¹. Notably, the detector demonstrates remarkable operational stability, maintaining its original X-ray response even after 6 months of unsealed storage in air, and can function effectively at elevated temperatures up to 100 °C, making it highly suitable for application in harsh environments. Moreover, the SC detector achieves high-resolution X-ray imaging because of its outstanding X-ray detection performance. This study not only verifies the feasibility of Cs₄MnBi₂Cl₁₂ SC for high-performance X-ray detection and imaging but also provides new design for preparation of eco-friendly X-ray detectors with both high sensitivity and stability.