Functionalizing surfaces by chemically attaching a layer of molecules to a surface in order to change its physical and chemical properties is key to many technology applications. Based on the vitally important water-repellent properties induced by superhydrophobic surfaces, we report the preparation and characterization of organophosphonate molecules self-assembled onto a hydrophilic plasma electrolytic oxidation (PEO) coated magnesium–lithium (Mg–Li) alloy surface. This superhydrophobic composite coating exhibits excellent nonwetting and superior corrosion resistance properties, making corrosive ions nearly nonpermeable. Moreover, the superhydrophobic composite coating does not deteriorate obviously after prolonged exposure in air, resulting in exceptional corrosion tolerance as well as long-term durability in air. This study enhances our understanding of combining the PEO technique with the self-assembly method in a complementary route, which shows great promise for delaying the onset of corrosion, thus shedding light on the potential applicability of the self-assembly of organic molecules on PEO coating surfaces of Mg–Li alloys.