High-level arsenic-containing wastewater (HAW) causes serious environmental pollution. Chemical precipitation is the most widely used technology for treating HAW. However, chemical precipitation generates huge amounts of hazardous solid wastes, which leads to secondary pollution. In this work, an efficient method, producing no secondary pollution was developed for one-step complete removal of As(V) from HAW using a hazardous solid waste namely arsenic-bearing gypsum (ABG). After the treatment, ABG was transformed into highly stable and environment-friendly mineral Johnbaumite. Meanwhile, the arsenic concentration in the wastewater decreased from 10,000 mg·L-1 to 0.22 mg·L-1 under optimized hydrothermal conditions (ABG dosage of 50 g·L-1, solution pH of 13.5, temperature of 150 °C for 12 h). The mechanism mainly included the following processes. (i) The phase transformation of ABG resulted in the release of calcium and hydrogen arsenate ions in ABG. (ii) Hydrogen arsenate ions transformed into arsenate ions in alkaline environment. (iii) Under alkaline conditions, calcium ions combined with arsenate ions to form Johnbaumite, whereas the hydrothermal conditions accelerated the crystal growth of Johnbaumite. This study provides a new idea for the synchronous treatment of toxic heavy metal-containing wastewaters and hazardous solid wastes.