<p>The effectiveness of cement in solidifying sludge contaminated with organic matter and heavy metals is often limited. To overcome this challenge, a novel treatment method combining an ionic soil stabilizer (ISS) with vacuum preloading was developed and systematically evaluated against the conventional cement-based approach. This study assessed the water stability of solidified sludge under repeated dry–wet cycles and conducted heavy metal leaching tests to evaluate performance. Key indicators such as cumulative relative mass loss, strength degradation, unconfined compressive strength, and the exudation behavior of heavy metals were analyzed to comprehensively determine the durability and stability of the solidified sludge. Results demonstrated that the ISS–vacuum preloading technique significantly outperformed the cement–vacuum preloading method, offering improved solidification strength and reduced environmental risk. The integration of an appropriate dosage of ISS notably enhanced the mechanical integrity and long-term immobilization of heavy metals, indicating its promising application in sustainable sludge stabilization.</p>