<p>This study employed bio-carbonated reactive magnesia cement (RMC) as a curing agent and polypropylene fibers as reinforcing and toughening materials to prepare fiber-reinforced bio-carbonated RMC fluidized solidified soil. Through flowability tests, rheological tests, triaxial shear tests, and a series of microscopic analyses including scanning electron microscope-energy dispersive spectroscopy, X-ray diffraction, fourier transform infrared spectroscopy, and thermogravimetry, the study systematically investigated the influence of RMC dosage, liquid-to-solid ratio, fiber content, and fiber length on the material’s workability and shear strength. Results indicate: Increasing RMC content promotes Mg(OH)₂ and hydrated magnesia carbonates formation, enhancing shear strength but reducing workability. Increasing the liquid-to-solid ratio improves workability but increases porosity, leading to reduced shear strength; increasing fiber content and length reduces flowability, but the resulting three-dimensional network structure effectively inhibits crack propagation, enhancing material toughness and shear strength. Within the study scope, maximum shear strength was achieved at a fiber content of 0.5% and length of 9 mm. Excessive fiber content or length tends to cause agglomeration, resulting in strength reduction. Microscopic analysis indicates that carbonation products effectively promote bonding between soil particles. This paper offers a theoretical basis for the application of fiber-reinforced bio-carbonated RMC fluidized solidified soil in geotechnical engineering.</p>