Due to the different chemical behaviors of arsenic (As) and cadmium (Cd), it is more difficult to use chemical methods to achieve the synergistic passivation of the two elements in farmland soil. This review summarizes the remediation materials and their efficiencies during the synergistic passivation of As and Cd in recent years. Combined passivators and modified passivators are widely applied, and the combined passivators, although their application is slightly complex, have a better passivative efficiency compared with the single one due to their simple preparation process. In the case of the nature of the passivative agents, the modified passivative agents have a good passivative effect with low concentration of application, but their preparation process is more complicated than that of the unmodified passivative agents, which restricts their wide use. Therefore, it is a breakthrough to simplify the preparation process of modified passivative agents for the synergistic passivation remediation of As and Cd in farmland soil. Additionally, the mechanisms regarding the synergistic passivation of As and Cd are summarized in terms of adsorption, chemical precipitation, complexation and chelation. Moreover, a case study related to synergistic passivation remediation of As and Cd in soil is introduced. Finally, five scientific questions concerning the synergistic passivation remediation of As and Cd in farmland soil are proposed, including the effectiveness, persistence, safety, universality and economy of passivative agents. The future prospects are also addressed, including the promotion of universality in application of passivative materials, their application amount, persistence and ecological risk to soil ecosystem, as well as the remediation pattern, standardization and regulation during the application of passivative material.