With the development of industry and agriculture, the increasingly serious problems of environmental pollution and water quality deterioration that affect human health need to be solved. Materials containing both Fe and Mn, the two most abundant metal elements, have been widely used for wastewater decontamination since they are nontoxic, low-cost, easy to prepare, and highly efficient. This review systematically summarizes the synthesis methods of Fe–Mn-based unloaded materials (such as spinel-type, perovskite-type, layered double hydroxides, metal–organic framework, and its derivatives) and loaded materials (carbon materials, oxides, and other loaded materials). Furthermore, the progress and problems of the application of Fe–Mn-based materials in the fields of Fenton, photo-Fenton, electro-Fenton, persulfate, and sulfite catalysis processes are analyzed. Different activation mechanisms of Fe–Mn-based materials, such as radical pathways and nonradical pathways (like direct electron transfer pathways, singlet oxygen, and high valence metals, etc.) are described. Finally, the application potential of Fe–Mn-based materials in environmental remediation is clarified and the future research directions are pointed out. It is expected that this review can provide new inspiration for subsequent research on the application of Fe–Mn based materials for wastewater treatment.