Abstract: Uranium (U) contamination in soils surrounding uranium mining and tailings disposal areas has become a significant environmental issue due to its long-term persistence, ecological toxicity, and potential risks to human health. Phytoremediation is considered a promising and environmentally friendly approach for remediating uranium-contaminated soils. However, the low bioavailability of uranium, which predominantly exists in stable geochemical fractions, greatly limits plant uptake efficiency. Iminodisuccinic acid (IDS), a biodegradable chelating agent with low environmental risk and strong metal-complexing capacity, has shown considerable potential for enhancing phytoextraction. Sorghum sudanense, characterized by rapid growth, high biomass production, and a well-developed root system, is considered a suitable candidate for the phytoremediation of uranium-contaminated soils. In this study, a pot experiment was conducted to investigate the effects of IDS on uranium migration, transformation, and accumulation by Sorghum sudanense grown in uranium-contaminated soil collected from a mining area in Jiangxi Province, China. The soil contained 297.83 ± 3.24 mg/kg uranium with an initial pH of 5.86. Four IDS application rates (0, 2, 5, and 10 mmol/kg) were established, and IDS was applied after 30 days of plant growth, and plants were harvested on day 50. Plant biomass, uranium accumulation, soil pH, and uranium fraction distribution were measured to evaluate the remediation performance. The results showed that appropriate IDS application significantly enhanced plant growth and uranium uptake. Among all treatments, the 5 mmol/kg IDS exhibited the best overall performance. Compared with the control without IDS, root and shoot biomass increased by 13.14% and 7.80%, respectively, while uranium concentration in shoots reached 46.66 mg/kg, representing a 1.51-fold increase over the control. In addition, IDS promoted the transformation of uranium from stable fractions to more bioavailable forms. Under the 5 mmol/kg IDS treatment, the proportion of residual uranium decreased by 57.85% compared with the control, whereas the proportion of amorphous Fe–Mn oxide-bound uranium increased by 8.50%, indicating enhanced uranium mobility and bioavailability. When the IDS dosage increased to 10 mmol/kg, the proportion of active uranium fractions further increased; however, plant biomass and uranium translocation efficiency declined, suggesting that excessive activation of uranium may impose physiological stress on plants and hinder uranium transport from roots to shoots. Overall, IDS effectively enhanced uranium bioavailability and improved its uptake by Sorghum sudanense. The optimal IDS dosage was identified as 5 mmol/kg, at which uranium activation and plant uptake reached a favorable balance. These findings provide new insights into the coupling mechanisms between biodegradable chelating agents and phytoremediation, and offer a reference for the remediation of such contaminated soils and the ecological restoration of mining areas.