Self-compacting concrete, owing to its flowability, filling ability, and self-compaction under its own weight, has been widely used in structures with densely arranged reinforcement. Previous studies have shown that wollastonite can affect the workability, mechanical strength, and durability indices of concrete by modifying the cementitious matrix structure. However, the simultaneous relationship among rheological behavior, microstructure, and resistance to chloride-ion transport in wollastonite-containing SCC has received limited attention. In this study, the effects of partial cement replacement with wollastonite on the rheological behavior, mechanical properties, resistance to chloride-ion transport, and microstructural characteristics of SCC were investigated. Six mixtures incorporating 0, 5, 10, 15, 20, and 25% wollastonite as a mass replacement of cement were prepared. As the replacement level increased from 0 to 25%, the slump-flow diameter decreased from 750 to 660 mm, while the V-Funnel time increased from 6 to 11 s. The L-Box ratio decreased from 0.9 to 0.8, whereas the U-Box height difference increased from 10 to 15 mm. Nevertheless, all mixtures maintained the required performance criteria for SCC. The mixture containing 20% wollastonite exhibited the best overall performance, with compressive strength increases of 20.45%, 14.25%, and 13.8% at 7, 28, and 90 days, respectively, compared with the reference mixture. Water absorption decreased by 21.34% and 20.65% at 28 and 90 days, respectively, while chloride-ion penetration decreased by 19.9% and 24.64% over the same periods. Resistance to freeze–thaw cycles also increased by 28.6% and 27.3% at 28 and 90 days, respectively. SEM images confirmed the formation of a denser matrix, reduced pore volume, and improved continuity of hydration products. Overall, the incorporation of wollastonite at an optimum replacement level improved the mechanical performance and durability of SCC through modification of rheological behavior and refinement of the microstructure